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Residues of polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs) and organochlorine pesticides in organically-farmed vegetables
Chemosphere 63 (2006) 541–553 www.elsevier.com/locate/chemosphere
Residues of polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs) and organochlorine pesticides in organically-farmed vegetables Azza Zohair a, Abou-Bakr Salim b, Adeola A. Soyibo c, Angus J. Beck a
c,*
Faculty of Specific Education, Home Economics Science Department, Menufiya Universty, Ashmoun, 32811 Menufiya, Egypt b Dairy Science Department, National Research Centre, Dokki, 12622 Cairo, Egypt c Department of Agricultural Sciences, Imperial College London, Wye Campus, Ashford, Kent TN25 5AH, United Kingdom Received 3 June 2005; received in revised form 15 September 2005; accepted 20 September 2005 Available online 16 November 2005
Abstract The residues of polyaromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs) and organochlorine pesticides (OCPs) in soils from organic farms and their uptake by four varieties of organic-produced potatoes and three varieties of organic carrots from England were investigated. Samples of the soils, crop peels and cores were all Soxhletextracted in triplicate, cleaned up by open-column chromatography and analysed by a multi-residue analytical method using gas chromatography with mass selective detection. The concentrations of PAHs, PCBs and OCPs in soils from organic farms ranged from 590 ± 43 to 2301 ± 146 lg/kg, 3.56 ± 0.73 to 9.61 ± 1.98 lg/kg and 52.2 ± 4.9 to 478 ± 111 lg/kg, respectively. Uptake by different crop varieties were 8.42 ± 0.93 to 40.1 ± 4.9 lg/kg RPAHs, 0.83 ± 0.19 to 2.68 ± 0.94 lg/kg RPCBs and 8.09 ± 0.83 to 133 ± 27 lg/kg ROCPs. Residue uptake from soils depended on plant variety; Desiree potato and Nairobi carrot varieties were more susceptible to PAH contamination. Likewise, uptake of PCBs and OCPs depended on potato variety. There were significant positive correlations between the PCB and OCP concentrations (P < 0.05) in soils and carrots but no significant correlation was found between the concentrations of any contaminants in soils and potatoes. Peeling carrots and potatoes was found to remove 52–100% of the contaminant residues depending on crop variety and the properties of the contaminants. Soil–crop bioconcentration factors (BCFs) decreased with increasing log Kow for PAHs up to about 4.5 and for PCBs up to about 6.5, above which no changes were discernible for either class of contaminants. No relationship was observed between soil–crop BCFs and log Kow for OCPs, most likely because their concentrations were low and variable. 2005 Elsevier Ltd. All rights reserved. Keywords: PAHs; PCBs; OCPs; Organic farms; Potatoes; Carrots
1. Introduction
*
Corresponding author. Tel.: +44 20 759 42621; fax: +44 20 759 42640. E-mail address: [email protected] (A.J. Beck).
Food quality and safety is a pertinent issue, consumers are concerned that their food should be both of high nutritional value and free from chemical residues. This has resulted in increasing demand for organic produce.
0045-6535/$ - see front matter 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.chemosphere.2005.09.012
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A. Zohair et al. / Chemosphere 63 (2006) 541–553
The global organic-food market is estimated to be worth United States $11 billion with the United Kingdom currently ranked fifth in terms of turnover for organic products, which in 1998/9 were valued at over one billion United States dollars (Garcia Martinez, 2004). The most important organic products in the European Union (EU) market are vegetables, fruits, milk products and cereals (Barrett et al., 2002). Organic farming approaches avoid the use of synthetic fertilizers and pesticides to reduce the potential for contamination of food with chemical residues (Gil et al., 2000), which is seen as an important point in their favour. However, like conventionally-farmed produce, organic crops are grown in soils that may be contaminated with persistent organic chemicals at low concentrations from past applications of agrochemicals or wastes, or from atmospheric deposition of volatile and semi-volatile organic compounds. In this respect, chemicals of concern would include polyaromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs) and organochlorine pesticides (OCPs). PAHs are naturally occurring contaminants formed by the incomplete combustion of organic materials (Smith, 1984). They comprise a large group of compounds (several hundreds) that contain two or more fused benzene rings; PAHs generally become more lipophilic, less soluble and less volatile with increasing molecular weight. Some of these compounds such as benzo[a]pyrene are known to be carcinogenic while others are suspected of being so (WHO, 1997; Schneider et al., 2000). The other contaminants considered here, PCBs and OCPs, are xenobiotic and have potential to persistence and bioaccumulation, and they have been reported to illicit adverse toxic effect on wildlife and humans. PCBs have been implicated in causing immune system disorders, dermatological problems, reproductive abnormalities, neuro-behavioral effects and cancer although conclusive cause and effect relationships are difficult to prove (Longnecker et al., 1997). Although production of PCBs and many organochlorine compounds has been banned widely for many years, their residues still remain as contaminants in the environment and food because of their long-term persistence and mobility (Rea, 1996; Lidstrom et al., 2002). The public need to be more fully aware of the issues related to contamination of organic-farmed crops if they are to make more informed choices regarding the value of organic produce relative to their conventionallyfarmed counterparts. Given the paucity of information about environmental organic pollutant residues in organically-farmed crops, this study aimed to investigate the residues of persistent potentially toxic and bioaccumulative organic compounds (namely PAHs, PCBs and OCPs) in soils and their uptake by organic-farmed carrots and potatoes.
2. Materials and methods 2.1. Soil and crop sampling and preparation Three carrot varieties (Nairobi, Major and Autumn Kings) and four potato varieties (Cara, Valour, Kestrel and Desiree) were obtained from organic farms in England. Three samples of each variety, and corresponding soils in which they were grown, were randomly collected from the field during harvest. Approximately 2 kg soil was taken from the cultivated horizon and thoroughly homogenized by grinding to pass a 2 mm sieve before taking sub-samples, which were stored in amber glass bottles in a freezer until analysis. Samples were taken from the field during a long dry spell, so no drying was necessary, and care was taken to collect soil immediately surrounding the potatoes and carrots sampled to avoid problems of spatial distribution of chemical residues. Potato and carrot samples were carefully washed with distilled water to remove any traces of soil before peeling with a vegetable peeler to a depth of 2 mm. The peel and the core were separately homogenized using a food processor and packed in amber glass bottles and stored in a freezer until analysis. 2.2. Chemicals and surrogate standards PCB standards of di-, tri-, terra-, penta-, hexa-, hepta-, octa-, nona- and decachlorinated biphenyls: 13 C-PCB28, 13C-PCB52, 13C-PCB101, 13C-PCB138, 13 C-PCB153, 13C-PCB180 and 13C-PCB209; PAH standards of naphthalene, acenaphthylene, acenaphthen, fluorene, pheneanthrene, anthracene, fluoranthene, pyrene, benzo[a]anthracene, chrysene, benzo[a]fluoranthene, benzo[k]fluoranthene, benzo[a]pyrene indeno[1,2,3c,d]pyrene, acenanaphthalene-D8, fluoranthene-D10, phenanthene-D10, pyrene-D10, benzo[a]pyrene-D12 and benzo[g,h,i]-perylene-D12; and OCP standards of a-HCH, HCB, b-HCH, c-HCH, heptachlor, aldrin, heptachlor-endo-epoxide, dieldrin, 4,4 0 DDE, endrin, bendosulfan, 4,4 0 DDD, 2,4 0 -DDT, 4,4 0 -DDT and methoxychlor were purchased from Qmx Laboratories Ltd. All solvents used were obtained from Rathburns Chemicals Ltd. Copper turnings and anhydrous sodium sulphate were supplied by Fisher chemicals. 2.3. Extraction, clean-up and analysis All three classes of analytes were quantified from a single Soxhlet extract of each soil and crop sample. In brief, 30 g each of soil or crop sample was mixed with 90 g of anhydrous sodium sulphate, spiked with 25 ll, 30 ll and 500 ll surrogate 13CPCBs, D-PAHs and OCP standards, respectively, and placed in pre-extracted Whatman extraction thimbles (43 mm · 123 mm). The thimbles were placed into a 500 ml Quickfit Soxhlet unit
Table 1 PAH, PCB and OCP residues in organically-farmed soils Compounds
Mean residue concentrations (lg/kg ± SD, N = 3) Potato varieties Valour
Kestrel
Desiree
Major
Nairobi
5.28 ± 1.05 1.78 ± 0.35 70.69 ± 14 60.5 ± 10.0 8.90 ± 1.52 336.3 ± 64 318 ± 62.6 192.3 ± 38 99.5 ± 18.9 93.52 ± 18 343.4 ± 65 459.6 ± 89 148.6 ± 28 163 ± 31.9 2301 ± 146 0.358 ± 0.030 0.914 ± 0.082 0.030 ± 0.002 0.055 ± 0.020 0.200 ± 0.030 0.230 ± 0.020 0.160 ± 0.010 0.140 ± 0.010 <0.001 ppb 0.570 ± 0.330 0.072 ± 0.003 0.295 ± 0.015 0.740 ± 0.010 1.330 ± 0.300 0.610 ± 0.010 0.770 ± 0.012 <0.001 ppb 0.240 ± 0.050 0.063 ± 0.015 0.117 ± 0.048 – <0.001 ppb 0.007 ± 0.003
4.65 ± 0.72 4.23 ± 0.64 67.41 ± 12 161.2 ± 28 10.3 ± 2.00 262 ± 47.3 226 ± 40.2 131.9 ± 24 148.5 ± 25 143 ± 25.5 190.5 ± 37 267.7 ± 43 82.3 ± 14.3 111.6 ± 20 1811 ± 89 0.500 ± 0.120 0.330 ± 0.070 0.011 ± 0.050 0.053 ± 0.010 0.113 ± 0.029 0.176 ± 0.020 0.070 ± 0.013 0.084 ± 0.010 <0.001 ppb 0.339 ± 0.015 0.143 ± 0.030 0.371 ± 0.080 0.432 ± 0.060 0.580 ± 0.070 0.086 ± 0.013 0.253 ± 0.017 <0.001 ppb 0.136 ± 0.008 0.044 ± 0.007 0.070 ± 0.020 0.017 ± 0.002 <0.001 ppb 0.026 ± 0.003
0.679 ± 0.130 0.81 ± 0.15 16.56 ± 3.1 14.57 ± 3.0 1.254 ± 0.2 84.9 ± 16.3 74.3 ± 12.8 45.87 ± 8.7 54.3 ± 9.80 52.29 ± 10 55.53 ± 11 104.8 ± 19 26.36 ± 5.1 83.8 ± 14.6 616 ± 34.7 0.730 ± 0.110 0.280 ± 0.020 0.064 ± 0.020 0.141 ± 0.010 0.298 ± 0.017 0.199 ± 0.019 0.047 ± 0.013 0.045 ± 0.011 0.012 ± 0.001 0.205 ± 0.015 0.080 ± 0.012 0.248 ± 0.040 0.293 ± 0.043 0.374 ± 0.050 0.036 ± 0.003 0.200 ± 0.013 <0.001 ppb 0.029 ± 0.003 0.100 ± 0.040 0.090 ± 0.015 0.019 ± 0.002 <0.001 ppb 0.015 ± 0.001
0.760 ± 0.150 0.23 ± 0.05 33.74 ± 6.0 23.69 ± 4.2 2.80 ± 0.03 125.6 ± 25 114.8 ± 22 61.75 ± 10 25.72 ± 4.2 24.3 ± 3.61 127.6 ± 24 197 ± 32.0 46.17 ± 6.7 194 ± 33.2 978 ± 69.2 0.740 ± 0.200 0.153 ± 0.030 0.068 ± 0.013 0.090 ± 0.009 0.163 ± 0.020 0.252 ± 0.040 0.013 ± 0.001 0.740 ± 0.030 0.017 ± 0.003 0.102 ± 0.015 0.270 ± 0.050 0.780 ± 0.190 0.640 ± 0.110 0.970 ± 0.160 0.036 ± 0.005 0.600 ± 0.100 <0.001 ppb 0.320 ± 0.040 0.270 ± 0.020 0.143 ± 0.020 0.070 ± 0.009 <0.001 ppb 0.250 ± 0.030
1.09 ± 0.180 1.91 ± 0.30 47.53 ± 9.2 39.76 ± 8.2 7.08 ± 2.25 196.6 ± 39 180.5 ± 36 108.2 ± 20 23.91 ± 4.3 24.63 ± 3.8 166 ± 30.4 129 ± 25.8 99.0 ± 18.1 189.5 ± 34 1215 ± 74 0.548 ± 0.009 0.278 ± 0.020 0.028 ± 0.018 0.057 ± 0.013 0.172 ± 0.021 0.678 ± 0.120 0.393 ± 0.040 0.411 ± 0.050 0.011 ± 0.002 1.689 ± 0.040 0.137 ± 0.020 0.644 ± 0.012 1.023 ± 0.350 1.920 ± 0.400 0.010 ± 0.001 0.485 ± 0.042 <0.001 ppb 0.433 ± 0.043 0.143 ± 0.002 0.432 ± 0.060 <0.001 ppb 0.007 ± 0.003 0.056 ± 0.010
0.400 ± 0.065 0.58 ± 0.11 16.84 ± 2.3 13.62 ± 1.5 3.94 ± 0.68 106.9 ± 18 91.78 ± 15 48.69 ± 7.6 8.89 ± 1.67 7.78 ± 1.24 46.86 ± 8.2 115.5 ± 20 27.88 ± 4.4 100 ± 18.1 589.7 ± 43 0.110 ± 0.020 0.032 ± 0.006 0.016 ± 0.002 0.013 ± 0.003 0.120 ± 0.010 0.194 ± 0.015 0.136 ± 0.013 0.144 ± 0.013 0.010 ± 0.002 0.969 ± 0.170 0.068 ± 0.015 0.283 ± 0.030 0.837 ± 0.200 1.630 ± 0.300 0.057 ± 0.007 0.373 ± 0.040 <0.001 ppb 0.288 ± 0.030 0.069 ± 0.005 0.041 ± 0.005 <0.001 ppb <0.001 ppb 0.067 ± 0.007
Autumn Kings
543
1.020 ± 0.180 2.64 ± 0.50 37.35 ± 7.4 10.28 ± 1.9 2.98 ± 0.55 215.2 ± 43 177.5 ± 34 115.5 ± 22 146 ± 28 141.8 ± 28 145.82 ± 27 291.5 ± 42 66.8 ± 13.2 112.9 ± 21 1467.2 ± 89 0.017 ± 0.004 0.171 ± 0.030 0.022 ± 0.002 0.022 ± 0.003 0.280 ± 0.050 0.169 ± 0.025 0.066 ± 0.007 0.078 ± 0.009 0.058 ± 0.008 0.990 ± 0.072 0.180 ± 0.030 0.347 ± 0.060 0.342 ± 0.050 0.559 ± 0.100 0.078 ± 0.002 0.316 ± 0.019 <0.001 ppb 0.206 ± 0.009 0.135 ± 0.004 0.038 ± 0.008 0.044 ± 0.003 0.008 ± 0.002 0.010 ± 0.006 (continued on next page)
A. Zohair et al. / Chemosphere 63 (2006) 541–553
Naphthalene Acenaphthylene Acen/fluorene Phenanthrene Anthracene Fluoranthene Pyrene Benzo[a]anthracene Benzo[b]fluoranthene Benzo[k]fluoranthene Benzo[a]pyrene Indeno[1,2,3-c,d]pyrene Dibenzo[a,h]anthracene Benzo[g,h,i]perylene RPAHs PCB28 PCB52 PCB44 PCB61 PCB66 PCB101 PCB99 PCB110 PCB82 PCB118 PCB151 PCB149 PCB153 PCB138 PCB183 PCB180 PCB188 PCB170 PCB201 PCB194 PCB208 PCB205 PCB206
Carrot varieties
Cara
544
Table 1 (continued) Compounds
Mean residue concentrations (lg/kg ± SD, N = 3) Potato varieties Cara
Valour
Kestrel
Desiree
Major
Nairobi
Autumn Kings
0.040 ± 0.010 6.94 ± 1.48 0.130 ± 0.033 0.150 ± 0.026 7.10 ± 1.34 6.30 ± 1.16 0.26 ± 0.04 <0.001 ppb 3.370 ± 0.570 6.600 ± 1.120 22.13 ± 4.00 0.330 ± 0.050 5.460 ± 1.070 20.43 ± 3.80 3.830 ± 0.670 2.360 ± 0.420 22.48 ± 3.70 5.400 ± 1.100 106.3 ± 13
0.032 ± 0.006 3.87 ± 0.80 0.130 ± 0.016 8.660 ± 1.400 2.300 ± 0.350 87.00 ± 16.20 1.600 ± 0.280 12.660 ± 1.900 3.970 ± 0.500 8.500 ± 1.100 177 ± 31.0 16.20 ± 2.70 13.06 ± 2.30 24.26 ± 4.10 1.06 ± 0.17 2.300 ± 0.560 44.36 ± 6.8 6.03 ± 0.83 409.1 ± 51
0.055 ± 0.004 3.56 ± 0.72 0.125 ± 0.040 0.300 ± 0.050 1.150 ± 0.170 1.640 ± 0.300 0.200 ± 0.030 0.344 ± 0.040 2.270 ± 0.360 11.730 ± 1.720 0.430 ± 0.060 31.000 ± 5.200 1.230 ± 0.210 15.100 ± 2.700 0.450 ± 0.068 1.200 ± 0.200 19.83 ± 3.10 1.830 ± 0.30 88.83 ± 12
0.236 ± 0.019 6.92 ± 1.40 0.167 ± 0.030 <0.001 ppb 7.900 ± 1.100 7.300 ± 1.200 0.300 ± 0.050 0.1 30 ± 0.026 3.500 ± 0.590 13.36 ± 2.30 18.630 ± 2.600 11.600 ± 1.890 1.830 ± 0.260 59.60 ± 7.80 18.90 ± 2.90 22.00 ± 3.20 152.4 ± 25 1.600 ± 0.210 319.2 ± 68
0.052 ± 0.008 9.607 ± 1.9 0.230 ± 0.034 0.830 ± 0.140 5.500 ± 1.100 5.000 ± 0.950 0.430 ± 0.068 1.600 ± 0.250 3.160 ± 0.570 0.570 ± 0.110 2.100 ± 0.380 22.70 ± 4.30 2.330 ± 0.410 19.56 ± 3.20 0.730 ± 0.120 1.160 ± 0.200 2.800 ± 0.530 5.600 ± 0.880 74.3 ± 8.10
0.056 ± 0.004 5.513 ± 1.1 1.215 ± 0.033 <0.001 ppb 4.330 ± 0.860 3.870 ± 0.660 1.346 ± 0.250 1.689 ± 0.280 1.098 ± 0.170 8.230 ± 1.360 2.300 ± 0.350 0.013 ± 0.002 6.770 ± 1.200 15.67 ± 2.40 <0.001 ppb 0.500 ± 0.090 2.050 ± 0.380 3.120 ± 0.560 52.2 ± 4.93
0.212 ± 0.032 4.348 ± 0.8 0.780 ± 0.130 4.260 ± 0.650 4.480 ± 1.440 8.060 ± 1.300 8.430 ± 1.200 4.300 ± 0.760 4.070 ± 0.610 2.860 ± 0.500 12.53 ± 2.10 6.100 ± 0.950 14.96 ± 1.98 127.6 ± 23 36.20 ± 6.80 34.56 ± 5.90 207.8 ± 31 1.300 ± 0.300 478.3 ± 111
A. Zohair et al. / Chemosphere 63 (2006) 541–553
PCB209 RPCBs HCB a-HCH b-HCH c-HCH Heptachlor Aldrin Heptachlor-endo-epoxide a-Endosulfan Dieldrin Endrin b-Endosulfan 4,4 0 DDE 4,4 0 ODD 2,4 0 -DDT 4,4 0 -DDT Methoxychlor ROCPs
Carrot varieties
Table 2 PAH, PCB and OCP residues in organically-farmed potatoes Compounds
Mean residue concentrations (lg/kg ± SD, N = 3) Potato varieties Cara
Kestrel
Desiree
Peel
Core
Peel
Core
Peel
Core
Peel
0.660 ± 0.132 0.310 ± 0.006 4.017 ± 0.800 3.200 ± 0.080 2.300 ± 0.360 1.210 ± 0.220 1.580 ± 0.310 0.360 ± 0.070 <0.010 ppb <0.010ppb 0.370 ± 0.060 0.372 ± 0.078 0.070 ± 0.013 0.580 ± 0.116 15.029 ± 1.264 0.139 ± 0.014 0.092 ± 0.025 0.025 ± 0.011 <0.001 ppb 0.011 ± 0.013 0.018 ± 0.002 <0.001 ppb 0.060 ± 0.009 <0.001 ppb 0.070 ± 0.030 <0.001 ppb 0.068 ± 0.030 0.116 ± 0.060 0.160 ± 0.060 <0.001 ppb 0.044 ± 0.017 <0.001 ppb <0.001 ppb 0.011 ± 0.005 0.068 ± 0.036 <0.001 ppb
0.230 ± 0.046 0.071 ± 0.014 2.850 ± 0.530 1.100 ± 0.020 0.500 ± 0.110 0.930 ± 0.176 0.880 ± 0.170 <0.01 ppb <0.01 ppb <0.01 ppb 0.169 ± 0.030 0.190 ± 0.035 0.032 ± 0.005 0.472 ± 0.090 7.423 ± 0.7662 <0.001 ppb 0.009 ± 0.003 0.004 ± 0.001 <0.001 ppb <0.001 ppb <0.001 ppb <0.001 ppb <0.001 ppb <0.001 ppb 0.030 ± 0.013 <0.001 ppb 0.010 ± 0.005 0.010 ± 0.006 0.016 ± 0.027 <0.001 ppb <0.001 ppb <0.001 ppb <0.001 ppb 0.005 ± 0.003 0.049 ± 0.010 <0.001 ppb
1.657 ± 0.320 1.366 ± 0.250 3.56 ± 0.620 3.68 ± 0.580 2.415 ± 0.430 3.48 ± 0.600 2.04 ± 0.410 0.797 ± 0.149 0.202 ± 0.040 0.201 ± 0.033 0.860 ± 0.152 0.158 ± 0.031 0.217 ± 0.034 0.697 ± 0.129 21.365 ± 1.314 0.267 ± 0.100 0.160 ± 0.050 <0.001 ppb 0.027 ± 0.006 0.064 ± 0.020 0.059 ± 0.018 0.009 ± 0.002 0.008 ± 0.002 <0.001 ppb 0.043 ± 0.019 0.020 ± 0.010 0.122 ± 0.050 0.096 ± 0.033 0.067 ± 0.023 0.015 ± 0.006 0.021 ± 0.006 <0.001 ppb 0.013 ± 0.005 <0.001 ppb 0.005 ± 0.002 <0.001 ppb
1.525 ± 0.300 <0.01 ppb 2.800 ± 0.450 2.780 ± 0.460 0.915 ± 0.163 1.750 ± 0.350 1.080 ± 0.210 0.240 ± 0.047 0.060 ± 0.012 0.142 ± 0.026 0.459 ± 0.081 0.109 ± 0.020 0.059 ± 0.011 0.395 ± 0.075 12.314 ± 0.984 0.030 ± 0.013 0.010 ± 0.001 <0.001 ppb <0.001 ppb 0.019 ± 0.007 0.018 ± 0.007 <0.001 ppb 0.003 ± 0.001 <0.001 ppb 0.011 ± 0.004 0.006 ± 0.002 0.014 ± 0.006 0.010 ± 0.005 0.008 ± 0.003 <0.001 ppb <0.001 ppb <0.001 ppb <0.001 ppb <0.001 ppb <0.001 ppb <0.001 ppb
0.053 ± 0.010 0.035 ± 0.006 1.230 ± 0.236 1.460 ± 0.250 0.074 ± 0.014 1.340 ± 0.240 1.210 ± 0.220 0.450 ± 0.085 <0.01 ppb <0.01 ppb <0.01 ppb <0.01 ppb <0.01 ppb <0.01 ppb 5.852 ± 0.599 0.314 ± 0.060 0.200 ± 0.050 0.030 ± 0.006 0.046 ± 0.007 0.165 ± 0.060 0.056 ± 0.120 0.010 ± 0.009 0.015 ± 0.001 <0.001 ppb 0.039 ± 0.012 0.013 ± 0.001 0.053 ± 0.020 0.041 ± 0.016 0.042 ± 0.015 0.006 ± 0.002 0.023 ± 0.001 <0.001 ppb 0.009 ± 0.060 0.013 ± 0.004 0.011 ± 0.005 <0.001 ppb
<0.01 ppb <0.01 ppb 0.370 ± 0.070 0.610 ± 0.090 <0.01 ppb 1.070 ± 0.214 0.490 ± 0.095 0.025 ± 0.004 <0.01 ppb <0.01 ppb <0.01 ppb <0.01 ppb <0.01 ppb <0.01 ppb 2.565 ± 0.331 0.180 ± 0.050 0.071 ± 0.020 0.021 ± 0.007 0.024 ± 0.005 0.078 ± 0.020 0.005 ± 0.001 0.004 ± 0.001 0.004 ± 0.001 <0.001 ppb 0.010 ± 0.002 0.009 ± 0.002 0.004 ± 0.001 0.010 ± 0.003 0.011 ± 0.003 <0.001 ppb <0.001 ppb <0.001 ppb <0.001 ppb <0.001 ppb 0.005 ± 0.001 <0.001 ppb
0.100 ± 0.012 <0.01 ppb 6.240 ± 2.100 4.960 ± 0.670 1.126 ± 0.320 4.600 ± 1.650 1.710 ± 0.330 0.480 ± 0.090 <0.01 ppb <0.01 ppb 0.055 ± 0.010 0.184 ± 0.030 0.730 ± 0.220 0.422 ± 0.110 20.607 ± 2.189 0.250 ± 0.080 0.080 ± 0.004 0.028 ± 0.008 0.050 ± 0.008 0.095 ± 0.021 0.122 ± 0.030 <0.001 ppb 0.026 ± 0.010 <0.001 ppb 0.054 ± 0.015 0.078 ± 0.030 0.330 ± 0.090 0.310 ± 0.130 0.217 ± 0.060 0.007 ± 0.001 0.105 ± 0.030 <0.001 ppb <0.001 ppb 0.014 ± 0.005 0.012 ± 0.004 <0.001 ppb
Core
545
0.042 ± 0.010 <0.01 ppb 3.600 ± 0.860 3.320 ± 0.580 0.158 ± 0.280 2.320 ± 0.410 0.600 ± 0.070 0.370 ± 0.120 <0.01 ppb <0.01 ppb <0.01 ppb <0.01 ppb 0.022 ± 0.006 0.114 ± 0.020 10.546 ± 1.300 0.137 ± 0.040 0.063 ± 0.020 0.016 ± 0.008 <0.001 ppb 0.030 ± 0.005 0.080 ± 0.020 <0.001 ppb 0.011 ± 0.005 <0.001 ppb 0.010 ± 0.004 0.024 ± 0.006 0.190 ± 0.040 0.150 ± 0.030 0.130 ± 0.030 <0.001 ppb 0.050 ± 0.014 <0.001 ppb <0.001 ppb 0.007 ± 0.004 0.006 ± 0.003 <0.001 ppb (continued on next page)
A. Zohair et al. / Chemosphere 63 (2006) 541–553
Naphthalene Acenaphthylene Acen/Fluorene Phenanthrene Anthracene Fluoranthene Pyrene Benzo[a]anthracene Benzo[b]fluoranthene Benzo[k]fluoranthene Benzo[a]pyrene Indeno[1,2,3-c,d]pyrene Dibenzo[a,h]anthracene Benzo[g,h,i]perylene RPAHs PCB28 PCB52 PCB44 PCB61 PCB66 PCB101 PCB99 PCB110 PCB82 PCB118 PCB151 PCB149 PCB153 PCB138 PCB183 PCB180 PCB188 PCB170 PCB201 PCB194 PCB208
Valour
546
Table 2 (continued) Compounds
Mean residue concentrations (lg/kg ± SD, N = 3) Potato varieties Cara
Kestrel
Desiree
Peel
Core
Peel
Core
Peel
Core
Peel
Core
<0.001 ppb <0.001 ppb 0.027 ± 0.010 0.909 ± 0.223 <0.001 ppb <0.001 ppb <0.001 ppb 0.560 ± 0.112 <0.001 ppb <0.001 ppb 1.230 ± 0.240 3.230 ± 0.460 0.860 ± 0.170 <0.001 ppb <0.001 ppb 1.460 ± 0.290 0.067 ± 0.012 <0.001 ppb 0.160 ± 0.030 0.300 ± 0.050 7.867 ± 0.965
<0.001 ppb <0.001 ppb <0.001 ppb 0.133 ± 0.041 <0.001 ppb <0.001 ppb <0.001 ppb 0.100 ± 0.018 <0.001 ppb <0.001 ppb <0.001 ppb 1.930 ± 0.380 <0.001 ppb <0.001 ppb <0.001 ppb 0.460 ± 0.062 <0.001 ppb <0.001 ppb <0.001 ppb <0.001 ppb 2.49 ± 0.538
<0.001 ppb <0.001 ppb <0.001 ppb 0.996 ± 0.237 <0.001 ppb <0.001 ppb <0.001 ppb 3.660 ± 0.630 0.430 ± 0.070 <0.001 ppb 1.900 ± 0.300 <0.001 ppb 24.000 ± 3.900 10.860 ± 1.870 2.130 ± 0.320 13.130 ± 2.100 0.330 ± 0.055 0.266 ± 0.030 3.670 ± 0.400 4.130 ± 0.720 64.506 ± 7.720
<0.001 ppb <0.001 ppb <0.001 ppb 0.129 ± 0.036 <0.001 ppb <0.001 ppb <0.001 ppb 0.330 ± 0.040 0.300 ± 0.040 <0.001 ppb <0.001 ppb <0.001 ppb 14.800 ± 2.320 5.460 ± 1.000 <0.001 ppb 0.230 ± 0.040 <0.001 ppb <0.001 ppb 0.430 ± 0.080 2.300 ± 0.370 23.85 ± 4.188
<0.001 ppb 0.008 ± 0.003 <0.001 ppb 1.094 ± 0.245 <0.001 ppb <0.001 ppb 0.270 ± 0.035 0.159 ± 0.025 0.067 ± 0.010 0.119 ± 0.020 0.830 ± 0.120 2.500 ± 0.330 0.088 ± 0.013 13.300 ± 2.100 0.023 ± 0.003 1.430 ± 0.230 0.012 ± 0.002 0.330 ± 0.060 1.330 ± 0.220 0.600 ± 0.100 21.058 ± 3.649
<0.001 ppb <0.001 ppb <0.001 ppb 0.436 ± 0.115 <0.001 ppb <0.001 ppb <0.001 ppb <0.001 ppb <0.001 ppb 0.019 ± 0.003 0.370 ± 0.050 0.042 ± 0.006 0.015 ± 0.003 4.900 ± 0.700 <0.001 ppb 0.100 ± 0.016 <0.001 ppb <0.001 ppb 0.260 ± 0.050 <0.001 ppb 5.706 ± 1.347
<0.001 ppb <0.001 ppb <0.001 ppb 1.778 ± 0.417 0.033 ± 0.004 <0.001 ppb 0.960 ± 0.180 1.070 ± 0.200 0.026 ± 0.003 <0.001 ppb 1.100 ± 0.230 2.100 ± 0.310 12.200 ± 2.500 0.167 ± 0.034 1.530 ± 0.250 12.430 ± 2.430 1.930 ± 0.260 1.930 ± 0.280 13.900 ± 2.500 1.070 ± 0.180 50.446 ± 8.543
<0.001 ppb <0.001 ppb <0.001 ppb 0.904 ± 0.225 <0.001 ppb <0.001 ppb <0.001 ppb 0.570 ± 0.100 <0.001 ppb <0.001 ppb <0.001 ppb 0.026 ± 0.003 1.630 ± 0.240 0.006 ± 0.002 <0.001 ppb 0.167 ± 0.032 <0.001 ppb <0.001 ppb 1.820 ± 0.270 0.330 ± 0.036 4.549 ± 0.674
A. Zohair et al. / Chemosphere 63 (2006) 541–553
PCB205 PCB206 PCB209 RPCBs HCB a-HCH b-HCH c-HCH Heptachlor Aldrin Heptachlor-endo-epoxide a-Endosulfan Dieldrin Endrin b-Endosulfan 4,4 0 DDE 4,4 0 DDD 2,4 0 -DDT 4,4 0 -DDT Methoxychlor ROCPs
Valour
Table 3 PAH, PCB and OCP residues in organically-farmed carrots Compounds
Mean residue concentrations (lg/kg ± SD, N = 3) Carrot varieties Major
Autumn Kings
Core
Peel
Core
Peel
0.137 ± 0.028 0.060 ± 0.013 1.436 ± 0.190 1.270 ± 0.180 1.470 ± 0.210 5.430 ± 1.230 2.543 ± 0.720 0.673 ± 0.220 0.270 ± 0.070 0.278 ± 0.030 0.530 ± 0.015 0.229 ± 0.010 1.100 ± 0.190 0.550 ± 0.012 14.976 ± 1.415 0.300 ± 0.120 0.055 ± 0.020 0.019 ± 0.005 0.032 ± 0.012 0.070 ± 0.028 0.154 ± 0.060 0.006 ± 0.013 0.077 ± 0.009 <0.001 ppb 0.176 ± 0.030 0.018 ± 0.005 0.131 ± 0.011 0.076 ± 0.008 0.291 ± 0.100 <0.001 ppb 0.032 ± 0.006 <0.001 ppb 0.041 ± 0.014 0.081 ± 0.025 0.232 ± 0.008 <0.001 ppb <0.001 ppb
0.051 ± 0.009 0.018 ± 0.004 0.480 ± 0.100 0.860 ± 0.260 0.757 ± 0.200 1.153 ± 0.180 0.095 ± 0.016 0.053 ± 0.011 0.093 ± 0.015 0.094 ± 0.015 0.134 ± 0.010 0.079 ± 0.012 <0.01 ppb 0.072 ± 0.013 3.938 ± 0.375 0.230 ± 0.090 0.015 ± 0.004 0.008 ± 0.002 0.0153 ± 0.006 0.020 ± 0.007 0.021 ± 0.006 <0.001 ppb <0.001 ppb <0.001 ppb <0.001 ppb <0.001 ppb <0.001 ppb <0.001 ppb 0.024 ± 0.005 <0.001 ppb 0.020 ± 0.003 <0.001 ppb <0.001 ppb 0.006 ± 0.002 0.066 ± 0.014 <0.001 ppb <0.001 ppb
0.036 ± 0.005 0.027 ± 0.005 1.030 ± 0.210 1.064 ± 0.280 1.850 ± 0.320 9.826 ± 1.690 <0.01 ppb 0.296 ± 0.049 0.424 ± 0.074 0.400 ± 0.070 0.310 ± 0.062 0.193 ± 0.028 0.169 ± 0.030 0.386 ± 0.070 16.011 ± 2.551 0.070 ± 0.013 0.013 ± 0.004 0.010 ± 0.003 <0.001 ppb 0.076 ± 0.021 0.060 ± 0.018 0.024 ± 0.006 0.034 ± 0.013 <0.001 ppb 0.100 ± 0.004 <0.001 ppb 0.070 ± 0.030 0.154 ± 0.045 0.280 ± 0.007 <0.001 ppb 0.035 ± 0.005 <0.001 ppb 0.014 ± 0.003 <0.001 ppb 0.008 ± 0.002 <0.001 ppb <0.001 ppb
0.012 ± 0.002 <0.01 ppb 0.520 ± 0.100 0.438 ± 0.860 0.612 ± 0.120 2.926 ± 0.480 <0.01 ppb 0.045 ± 0.009 0.168 ± 0.030 0.167 ± 0.028 0.1 88 ± 0.035 <0.01 ppb <0.01 ppb <0.01 ppb 5.076 ± 0.767 0.034 ± 0.011 0.006 ± 0.002 <0.001 ppb <0.001 ppb 0.039 ± 0.006 0.005 ± 0.003 <0.001 ppb 0.004 ± 0.001 <0.001 ppb 0.025 ± 0.005 <0.001 ppb 0.006 ± 0.002 0.005 ± 0.001 0.017 ± 0.005 <0.001 ppb <0.001 ppb <0.001 ppb <0.001 ppb <0.001 ppb 0.003 ± 0.001 <0.001 ppb <0.001 ppb
0.673 ± 0.130 1.135 ± 0.227 3.120 ± 0.620 1.690 ± 0.200 0.913 ± 0.180 16.530 ± 3.100 1.1660 ± 0.233 0.875 ± 0.175 1.290 ± 0.256 1.194 ± 0.218 1.900 ± 0.350 0.800 ± 0.140 0.476 ± 0.090 0.510 ± 0.100 32.272 ± 4.151 0.006 ± 0.002 0.018 ± 0.002 0.015 ± 0.003 0.005 ± 0.002 0.120 ± 0.019 0.043 ± 0.012 0.004 ± 0.001 0.046 ± 0.013 0.007 ± 0.003 0.010 ± 0.002 0.009 ± 0.004 0.090 ± 0.013 0.070 ± 0.021 0.109 ± 0.030 0.018 ± 0.004 0.029 ± 0.006 <0.001 ppb 0.047 ± 0.008 0.008 ± 0.003 <0.001 ppb <0.001 ppb <0.001 ppb
Core 0.550 ± 0.120 <0.01 ppb 1.540 ± 0.440 0.880 ± 0.160 0.520 ± 0.130 2.940 ± 0.580 0.166 ± 0.032 <0.01 ppb 0.212 ± 0.040 0.187 ± 0.034 0.588 ± 0.115 0.148 ± 0.027 0.072 ± 0.014 0.041 ± 0.008 7.804 ± 0.806 <0.001 ppb 0.013 ± 0.005 <0.001 ppb <0.001 ppb 0.050 ± 0.006 0.022 ± 0.004 <0.001 ppb 0.005 ± 0.002 <0.001 ppb 0.003 ± 0.001 <0.001 ppb 0.010 ± 0.003 0.010 ± 0.002 0.030 ± 0.004 <0.001 ppb <0.001 ppb <0.001 ppb 0.006 ± 0.002 0.003 ± 0.001 <0.001 ppb <0.001 ppb <0.001 ppb (continued on next page)
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Naphthalene Acenaphthylene Acen/Fluorene Phenanthrene Anthracene Fluoranthene Pyrene Benzo[a]anthracene Benzo[b]fluoranthene Benzo[k]fluoranthene Benzo[a]pyrene Indeno[1,2,3-c,d]pyrene Dibenzo[a,h]anthracene Benzo[g,h,i]perylene RPAHs PCB28 PCB52 PCB44 PCB61 PCB66 PCB101 PCB99 PCB110 PCB82 PCB118 PCB151 PCB149 PCB153 PCB138 PCB183 PCB180 PCB188 PCB170 PCB201 PCB194 PCB208 PCB205
Nairobi
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Table 3 (continued) Compounds
Mean residue concentrations (lg/kg ± SD, N = 3) Carrot varieties
PCB206 PCB209 RPCBs HCB a-HCH b-HCH c-HCH Heptachlor Aldrin Heptachlor-endo-epoxide a-Endosulfan Dieldrin Endrin b-Endosulfan 4,4 0 DDE 4,4 0 DDD 2,4 0 -DDT 4,4 0 -DDT Methoxychlor ROCPs
Nairobi
Autumn Kings
Peel
Core
Peel
Core
Peel
Core
0.007 ± 0.002 0.007 ± 0.003 1.805 ± 0.393 0.100 ± 0.020 0.200 ± 0.037 <0.001 ppb <0.001 ppb 0.200 ± 0.030 0.140 ± 0.023 1.930 ± 0.350 0.030 ± 0.005 1.300 ± 0.210 7.320 ± 1.400 0.009 ± 0.002 0.860 ± 0.140 0.100 ± 0.019 0.280 ± 0.048 1.300 ± 0.240 2.700 ± 0.440 16.469 ± 2.081
<0.001 ppb <0.001 ppb 0.425 ± 0.132 0.050 ± 0.010 0.100 ± 0.019 <0.001 ppb <0.001 ppb <0.001 ppb 0.013 ± 0.002 1.020 ± 0.017 <0.001 ppb 0.030 ± 0.004 3.400 ± 0.650 0.006 ± 0.001 0.017 ± 0.003 0.010 ± 0.002 0.150 ± 0.030 0.900 ± 0.150 <0.001 ppb 5.696 ± 0.969
<0.001 ppb <0.001 ppb 0.948 ± 0.238 0.260 ± 0.035 <0.001 ppb 2.070 ± 0.038 0.230 ± 0.034 0.200 ± 0.036 0.270 ± 0.500 0.490 ± 0.078 <0.001 ppb 1.760 ± 0.300 0.006 ± 0.001 0.009 ± 0.003 0.500 ± 0.120 <0.001 ppb 0.350 ± 0.050 0.520 ± 0.110 0.240 ± 0.045 6.905 ± 0.714
<0.001 ppb <0.001 ppb 0.144 ± 0.041 0.140 ± 0.018 < 0.001 ppb 0.330 ± 0.053 0.150 ± 0.030 0.027 ± 0.005 0.125 ± 0.023 0.021 ± 0.004 <0.001 ppb 0.100 ± 0.020 <0.001 ppb 0.004 ± 0.001 <0.001 ppb <0.001 ppb 0.180 ± 0.036 0.110 ± 0.022 <0.001 ppb 1.187 ± 0.113
<0.001 ppb 0.020 ± 0.005 0.674 ± 0.147 0.330 ± 0.053 2.860 ± 0.520 <0.001 ppb 5.100 ± 1.030 5.050 ± 0.900 2.900 ± 0.480 1.670 ± 0.330 1.270 ± 0.230 2.900 ± 0.470 0.590 ± 0.120 6.160 ± 0.960 36.600 ± 6.300 3.830 ± 0.660 8.000 ± 1.400 47.760 ± 9.200 0.730 ± 0.140 125.750 ± 26.070
<0.001 ppb <0.001 ppb 0.152 ± 0.044 0.036 ± 0.006 0.100 ± 0.020 <0.001 ppb 0.400 ± 0.070 <0.001 ppb 0.660 ± 0.120 0.560 ± 0.110 0.200 ± 0.032 0.900 ± 0.150 <0.001 ppb <0.001 ppb 1.360 ± 0.240 0.700 ± 0.130 0.330 ± 0.630 1.600 ± 0.320 0.430 ± 0.080 7.276 ± 1.106
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Major
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and extracted for 24 h with 300 ml of hexane:acetone (1:1). Extracts were then reduced to near dryness on a rotary film evaporator (Buchi R-124), taken up in 10 ml hexane and transferred into pre-washed and baked glass vials. The samples were then reduced farther on a Techne Dri-Block under a gentle stream of N2 to 2 ml. The extracts were cleaned by passing through Bakerbond PCB-A SPE cartridges pre-conditioned with 10 ml hexane. They were again reduced under N2 to near dryness, transferred to clean glass vials and made up to 1 ml for analysis. One microlitre of each clean sample extract was injected into an Hewlett Packard 6890 gas chromatograph fitted with a 30 m HP5-MS fused silica capillary column (30 · 0.25 mm · 0.25 lm film thickness) and connected to an Hewlett Packard 5973 mass selective detector. The carrier gas was helium, maintained at a flow rate of 1.0 ml/min by electronic pneumatic control. The injection port temperature was 230 C with electron energy of 70 eV. The quadrupole temperature was 280 C. The instrument was tuned on PFTBA. The oven programme for all three classes of compounds was as follows: 100 C for 2 min, 5 C/min to 200 C for 6 min, 4 C/min to 280 C for 7 min, 90 C for 2 min, 10 C/min to 240 C, 3 C/min to 310 C for 5 min and 100 C for 2 min, 5 C/min to 200 C for 6 min, 4 C/min to 280 C for 2 min, respectively. Calibration was by seven external standards over the concentration ranges l–30 ng/ml for PCBs, 1– 1000 ng/ml for PAHs and 1–100 ng/ml for OCPs. The mass spectrometer was operated in selective ion monitoring mode using separate ions to identify and confirm compounds.
3. Results and discussion A multi-analytical method was developed for the analysis of PAHs, PCBs and OCPs in the same extract of plant and soil samples. Recoveries for surrogate D-PAHs in plant and soil ranged between 84% and 111% and between 90% and 115%, respectively, with low RSD% ranging from 3 to 12. Slightly lower recoveries (69–78%) of low molecular weight naphthalene were likely due to losses occurring during extraction and clean-up; this is typically reported (WHO, 1998). Mean recoveries of the 13C surrogate PCBs from soils ranged from 92% to 124% with RSD% ranging from 4 to 19. Mean recoveries of surrogate OCPs from plants and soils fell in the range 80–108% and 83–112%, respectively, with low RSD% ranging from 3 to 14. Such recoveries were in a similar range to those frequently reported for these three classes of compounds therefore we considered our own method to be reliable. Table 1 shows the PAH concentrations of the soils in which the organic potatoes and carrots investigated were grown. The most abundant individual PAH compound
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in soil investigated here was indeno[1,2,3-c,d]pyrene. Benzo[a]pyrene, fluoranthene, pyrene, benzo[a]anthracene and benzo[g,h,i]perylene were also relatively abundant reflecting their lower water solubility and lower vapour pressures. The soils RPAHs concentrations ranged from 590 ± 43 to 2301 ± 146 lg/kg. In both the peels and the cores of different potato varieties, the PAH burden was dominated by the low molecular weight compounds acenapthene/fluorine ranging from 1.6 ± 0.3 to 9.84 ± 2.9 lg/kg and phenanthrene in the range 2.07 ± 0.3 to 8.28 ± 1.3 lg/kg (Table 2). These compounds are more water-soluble and more volatile than the relatively high molecular weight PAHs, which were more abundant in soils (Table 1), therefore it is not surprising that they were more susceptible to crop uptake. The potatoes also contained relatively high amounts of fluoranthene and pyrene, reflecting their relatively high concentration in the crop-associated soils. The results in Table 3 also show that fluoranthene, ranging from 6.58 ± 1.4 to 19.5 ± 3.6 lg/kg, is the most abundant individual PAH compound detected in carrots. The concentrations of RPAHs in organic carrots ranged from 18.9 ± 0.79 to 40.1 ± 4.9 lg/kg and from 8.4 ± 0.93 to 33.7 ± 2.30 lg/kg in organic potatoes— markedly higher than the PAH concentrations in potatoes grown in conventional farms reported by Ladovici et al. (1995), Kazerouni et al. (2001) and Vikelsoe et al. (2002). However, in comparison to two studies in China the contaminant concentrations reported here were relatively low. Tao et al. (2004) reported that almost all 16 U.S.EPA-listed PAHs were found in root crops and that concentrations were 72 ng/g in a lesser contaminated area compared to 210 ng/g in root crops grown in soils close to an urban area and irrigated with wastewater. Amongst the PCBs, congener 138 was the most abundant in all tested samples except Kestrel potatoes and Autumn King carrots where congeners 28 and 118 were the highest, respectively. The results are in agreement with those reported by Theobald (2003) who found that PCB 138 was the most abundant congener in soils that they investigated. Organic vegetables investigated contained PCB levels ranging from 0.83 ± 0.19 to 2.68 ± 0.94 lg/kg, however, such levels do not give cause for concern in relation to the maximum UK tolerable daily intake limit of 10 pg/kg/body weight/day (Tao et al., 2004). Although organic farming avoids the use of pesticides, residues may remain from pre-organic farming applications or as a result of atmospheric deposition. DDT, endrin, c-HCH (lindane) and endosulfan were the most frequently detected OCPs in soils investigated here (Table 1). From Tables 2 and 3 it is evident that these OCP residues may transfer to crops, however, the levels detected were below the maximum residue limits (MRLs) of FAO/WHO (1993). Crop uptake of HCB was relatively low (<0.0010.037 lg/kg) in all tested
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samples but DDT levels ranged from 3.6 to 100 lg/kg, which might give cause for concern. Aldrin is converted to dieldrin by an epoxidation process in biological system (Rumsey and Bond, 1974) and therefore dieldrin is expected to be found in relatively higher concentrations than aldrin as we found in this study (Tables 1–3). There was a significant positive correlation (P < 0.05) between concentrations of PCBs and OCPs in soil and their uptake by carrots (Fig. 1) but no correlation was observed for PAHs with carrots or any of the compounds with any potato variety. This suggests that characteristics of the chemicals and the crop species were most important in determining uptake. Chiou et al. (2001) reported that plant lipids is the major factor causing observed differences in plant uptake of lipophilic contaminants such as aldrin, dieldrin, heptachlor and heptachlor-epoxide. Stronger correlations for carrots than potatoes may be explained by the presence of oil channels in carrots as previously suggested by WHO (1998) and Kipopoulou et al. (1999). Significant positive correlations (P < 0.05) were found between varieties and uptake; Desiree potato variety and Nairobi carrot variety were more susceptible to PAH contamination while Kestrel potato variety had high ability to uptake PCBs
and OCPs from contaminated soils. Gao and Zhu (2004) found that uptake, accumulation and translocation of phenanthrene and pyrene by 12 plant species grown in soils treated by different concentrations of phenanthrene and pyrene were correlated with their soil concentrations and also dependent on plant species. Characteristics of crop species that influence contaminant uptake is worthy of more detailed investigation. Soil–crop bioconcentration factors (BCFs) decreased with increasing log Kow for PAHs up to about 4.5 and for PCBs up to about 6.5, above which no changes were observed for either class of contaminants (Fig. 2). No relationship was observed between soil–crop BCFs and log Kow for OCPs, most likely because their concentrations were low and variable. In addition to characteristics of crops and physico-chemical properties of the chemical residues, soil–plant transfer of persistent organic chemical residues will depend on the physical and chemical characteristics of the soils in which they are grown. Organic matter content and moisture content are the soil factors most frequently reported to exert the greatest impact on availability of soil-sorbed nonionic organic chemical residues to uptake by crops (Beck et al., 1996). Generally, crop uptake would be favoured under
Fig. 1. Correlation between the concentrations of PCBs and OCPs in carrots and soils in which they were grown.
Fig. 2. Relationship between the crop:soil BCFs of PAHs and PCBs with their log Kow in Autumn King carrots (pyramids) and Valour potatoes (spheres). BCF = (P + C)/S = contaminant concentrations in peel + contaminant concentrations in core/contaminant concentrations in soils.
A. Zohair et al. / Chemosphere 63 (2006) 541–553
moist conditions in soils with low organic matter contents whereas in dry soils with high organic matter contents the chemical residues will be strongly bound by the soil retarding uptake. In this study the soil organic
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matter content ranged from 3% to 5% so they have been a factor in explaining the differences observed. Soil pH ranged from 6.5 to 7.6 but was not considered important given that the chemicals investigated are nonionic or only
Fig. 3. Comparison between the concentrations of PAHs, PCBs and OCPs in the peels and cores of carrots and potatoes.
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weakly ionic. Effectively, all of the aforementioned factors will combine in complex ways to control the uptake of the chemicals from the soils into the carrots and potatoes, however, caution needs to be exercised in considering the assertions made here because even where statistically significant differences were observed between crop residue concentrations it was impossible to ascertain the main factors responsible for these differences due to the limited number of samples available. From Fig. 3 it can be seen that PAHs, PCBs and OCPs are all much more abundant in the peels of both potatoes and carrots. This observation has been made by many researchers including OÕConnor et al. (1990); WHO (1998) and Wild and Jones (1992). Greater lipid content in potato peels than that in their corresponding cores were attributed by Chiou et al. (2001) and Fismes et al. (2002) to the higher lipid contents of the peels. Removal of organic pollutant residues from potato and carrot varieties after peeling ranged from 55.9% to 100%, 52% to 100% and 57.5% to 100% for PAHs, PCBs and OCPs, respectively. The potential for peel to core translocation depended on plant variety. For example, lowest PCBs removal by peeling was observed for Desiree potatoes (55.9–67.7%). This likely reflects the higher dry matter content of Desiree potatoes than any other crop investigated.
4. Concluding remarks Our results show that PAHs, PCBs and OCPs were taken up by carrots and potatoes from soils. Uptake depended on crop varieties but more research is needed to establish whether this was related to characteristics of the crops or if it was simply a reflection of spatial variability in the distribution of contaminant residues in the soils in which the different crops were grown. Both factors likely contributed because we observed that all contaminants were more abundant in the peels than the cores of all crop varieties reflecting higher peel lipid contents, and because PCB and OCP concentrations in crops were strongly correlated with their concentrations in associated soils. Most of the compounds considered here have been reported to have endocrine disrupting properties, and some are known or suspected carcinogens. Thus, their presence in food is of concern and intakes should be as low as reasonably practicable (COT, 1996). Food containing residues at or below the respective MRLs are considered to be toxicologically acceptable for long-term intake (White et al., 2002). On this basis, the concentrations of contaminant residues in the organic vegetables analysed here should not give cause for concern, however, it is possible that even such low levels of contaminants may merit more detailed scrutiny in the near future. For example, Pesticides Safety Directorate, 2001 and Codex Committee on
Pesticide Residue, 2001 have stated that the need for an Acute Reference Dose (ARfD) will be considered for all pesticides in the future, and the estimated short-term intake of pesticide residues will be compared with the ARfDs in order to interpret the possible risks associated with unit-to-unit, e.g. carrot to carrot, variability in residue levels (Renwick et al., 2003). Despite the complexity of risk assessment procedures and generally slow development and introduction of legislation in EU and elsewhere that will require their use in hazard assessment and human exposure management, it is clear that relatively simple procedures such as peeling root crops like carrots and potatoes can considerably reduce exposure. The more urgent need is for efforts to ensure that the general public are better informed about the risks from contaminants in foodstuffs and, in particular, how they can reduce their personal exposure by simple procedures such as adequate washing and peeling. This is particularly true with respects to environmental contaminants in organically-farmed vegetables where much of the public may be misinformed with regards to the relative safety of such products as compared to their conventionally-farmed counterparts. However, it should be stressed that the levels POPs in vegetables are low and can be reduced further by appropriate preparation and cooking. The risks to health that they may present are outweighed by the nutritional benefits of a healthy balanced diet including the recommended consumption of 5 portions of fruit and vegetables each day.
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Residues of polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs) and organochlorine pesticides in organically-farmed vegetables Azza Zohair a, Abou-Bakr Salim b, Adeola A. Soyibo c, Angus J. Beck a
c,*
Faculty of Specific Education, Home Economics Science Department, Menufiya Universty, Ashmoun, 32811 Menufiya, Egypt b Dairy Science Department, National Research Centre, Dokki, 12622 Cairo, Egypt c Department of Agricultural Sciences, Imperial College London, Wye Campus, Ashford, Kent TN25 5AH, United Kingdom Received 3 June 2005; received in revised form 15 September 2005; accepted 20 September 2005 Available online 16 November 2005
Abstract The residues of polyaromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs) and organochlorine pesticides (OCPs) in soils from organic farms and their uptake by four varieties of organic-produced potatoes and three varieties of organic carrots from England were investigated. Samples of the soils, crop peels and cores were all Soxhletextracted in triplicate, cleaned up by open-column chromatography and analysed by a multi-residue analytical method using gas chromatography with mass selective detection. The concentrations of PAHs, PCBs and OCPs in soils from organic farms ranged from 590 ± 43 to 2301 ± 146 lg/kg, 3.56 ± 0.73 to 9.61 ± 1.98 lg/kg and 52.2 ± 4.9 to 478 ± 111 lg/kg, respectively. Uptake by different crop varieties were 8.42 ± 0.93 to 40.1 ± 4.9 lg/kg RPAHs, 0.83 ± 0.19 to 2.68 ± 0.94 lg/kg RPCBs and 8.09 ± 0.83 to 133 ± 27 lg/kg ROCPs. Residue uptake from soils depended on plant variety; Desiree potato and Nairobi carrot varieties were more susceptible to PAH contamination. Likewise, uptake of PCBs and OCPs depended on potato variety. There were significant positive correlations between the PCB and OCP concentrations (P < 0.05) in soils and carrots but no significant correlation was found between the concentrations of any contaminants in soils and potatoes. Peeling carrots and potatoes was found to remove 52–100% of the contaminant residues depending on crop variety and the properties of the contaminants. Soil–crop bioconcentration factors (BCFs) decreased with increasing log Kow for PAHs up to about 4.5 and for PCBs up to about 6.5, above which no changes were discernible for either class of contaminants. No relationship was observed between soil–crop BCFs and log Kow for OCPs, most likely because their concentrations were low and variable. 2005 Elsevier Ltd. All rights reserved. Keywords: PAHs; PCBs; OCPs; Organic farms; Potatoes; Carrots
1. Introduction
*
Corresponding author. Tel.: +44 20 759 42621; fax: +44 20 759 42640. E-mail address: [email protected] (A.J. Beck).
Food quality and safety is a pertinent issue, consumers are concerned that their food should be both of high nutritional value and free from chemical residues. This has resulted in increasing demand for organic produce.
0045-6535/$ - see front matter 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.chemosphere.2005.09.012
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The global organic-food market is estimated to be worth United States $11 billion with the United Kingdom currently ranked fifth in terms of turnover for organic products, which in 1998/9 were valued at over one billion United States dollars (Garcia Martinez, 2004). The most important organic products in the European Union (EU) market are vegetables, fruits, milk products and cereals (Barrett et al., 2002). Organic farming approaches avoid the use of synthetic fertilizers and pesticides to reduce the potential for contamination of food with chemical residues (Gil et al., 2000), which is seen as an important point in their favour. However, like conventionally-farmed produce, organic crops are grown in soils that may be contaminated with persistent organic chemicals at low concentrations from past applications of agrochemicals or wastes, or from atmospheric deposition of volatile and semi-volatile organic compounds. In this respect, chemicals of concern would include polyaromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs) and organochlorine pesticides (OCPs). PAHs are naturally occurring contaminants formed by the incomplete combustion of organic materials (Smith, 1984). They comprise a large group of compounds (several hundreds) that contain two or more fused benzene rings; PAHs generally become more lipophilic, less soluble and less volatile with increasing molecular weight. Some of these compounds such as benzo[a]pyrene are known to be carcinogenic while others are suspected of being so (WHO, 1997; Schneider et al., 2000). The other contaminants considered here, PCBs and OCPs, are xenobiotic and have potential to persistence and bioaccumulation, and they have been reported to illicit adverse toxic effect on wildlife and humans. PCBs have been implicated in causing immune system disorders, dermatological problems, reproductive abnormalities, neuro-behavioral effects and cancer although conclusive cause and effect relationships are difficult to prove (Longnecker et al., 1997). Although production of PCBs and many organochlorine compounds has been banned widely for many years, their residues still remain as contaminants in the environment and food because of their long-term persistence and mobility (Rea, 1996; Lidstrom et al., 2002). The public need to be more fully aware of the issues related to contamination of organic-farmed crops if they are to make more informed choices regarding the value of organic produce relative to their conventionallyfarmed counterparts. Given the paucity of information about environmental organic pollutant residues in organically-farmed crops, this study aimed to investigate the residues of persistent potentially toxic and bioaccumulative organic compounds (namely PAHs, PCBs and OCPs) in soils and their uptake by organic-farmed carrots and potatoes.
2. Materials and methods 2.1. Soil and crop sampling and preparation Three carrot varieties (Nairobi, Major and Autumn Kings) and four potato varieties (Cara, Valour, Kestrel and Desiree) were obtained from organic farms in England. Three samples of each variety, and corresponding soils in which they were grown, were randomly collected from the field during harvest. Approximately 2 kg soil was taken from the cultivated horizon and thoroughly homogenized by grinding to pass a 2 mm sieve before taking sub-samples, which were stored in amber glass bottles in a freezer until analysis. Samples were taken from the field during a long dry spell, so no drying was necessary, and care was taken to collect soil immediately surrounding the potatoes and carrots sampled to avoid problems of spatial distribution of chemical residues. Potato and carrot samples were carefully washed with distilled water to remove any traces of soil before peeling with a vegetable peeler to a depth of 2 mm. The peel and the core were separately homogenized using a food processor and packed in amber glass bottles and stored in a freezer until analysis. 2.2. Chemicals and surrogate standards PCB standards of di-, tri-, terra-, penta-, hexa-, hepta-, octa-, nona- and decachlorinated biphenyls: 13 C-PCB28, 13C-PCB52, 13C-PCB101, 13C-PCB138, 13 C-PCB153, 13C-PCB180 and 13C-PCB209; PAH standards of naphthalene, acenaphthylene, acenaphthen, fluorene, pheneanthrene, anthracene, fluoranthene, pyrene, benzo[a]anthracene, chrysene, benzo[a]fluoranthene, benzo[k]fluoranthene, benzo[a]pyrene indeno[1,2,3c,d]pyrene, acenanaphthalene-D8, fluoranthene-D10, phenanthene-D10, pyrene-D10, benzo[a]pyrene-D12 and benzo[g,h,i]-perylene-D12; and OCP standards of a-HCH, HCB, b-HCH, c-HCH, heptachlor, aldrin, heptachlor-endo-epoxide, dieldrin, 4,4 0 DDE, endrin, bendosulfan, 4,4 0 DDD, 2,4 0 -DDT, 4,4 0 -DDT and methoxychlor were purchased from Qmx Laboratories Ltd. All solvents used were obtained from Rathburns Chemicals Ltd. Copper turnings and anhydrous sodium sulphate were supplied by Fisher chemicals. 2.3. Extraction, clean-up and analysis All three classes of analytes were quantified from a single Soxhlet extract of each soil and crop sample. In brief, 30 g each of soil or crop sample was mixed with 90 g of anhydrous sodium sulphate, spiked with 25 ll, 30 ll and 500 ll surrogate 13CPCBs, D-PAHs and OCP standards, respectively, and placed in pre-extracted Whatman extraction thimbles (43 mm · 123 mm). The thimbles were placed into a 500 ml Quickfit Soxhlet unit
Table 1 PAH, PCB and OCP residues in organically-farmed soils Compounds
Mean residue concentrations (lg/kg ± SD, N = 3) Potato varieties Valour
Kestrel
Desiree
Major
Nairobi
5.28 ± 1.05 1.78 ± 0.35 70.69 ± 14 60.5 ± 10.0 8.90 ± 1.52 336.3 ± 64 318 ± 62.6 192.3 ± 38 99.5 ± 18.9 93.52 ± 18 343.4 ± 65 459.6 ± 89 148.6 ± 28 163 ± 31.9 2301 ± 146 0.358 ± 0.030 0.914 ± 0.082 0.030 ± 0.002 0.055 ± 0.020 0.200 ± 0.030 0.230 ± 0.020 0.160 ± 0.010 0.140 ± 0.010 <0.001 ppb 0.570 ± 0.330 0.072 ± 0.003 0.295 ± 0.015 0.740 ± 0.010 1.330 ± 0.300 0.610 ± 0.010 0.770 ± 0.012 <0.001 ppb 0.240 ± 0.050 0.063 ± 0.015 0.117 ± 0.048 – <0.001 ppb 0.007 ± 0.003
4.65 ± 0.72 4.23 ± 0.64 67.41 ± 12 161.2 ± 28 10.3 ± 2.00 262 ± 47.3 226 ± 40.2 131.9 ± 24 148.5 ± 25 143 ± 25.5 190.5 ± 37 267.7 ± 43 82.3 ± 14.3 111.6 ± 20 1811 ± 89 0.500 ± 0.120 0.330 ± 0.070 0.011 ± 0.050 0.053 ± 0.010 0.113 ± 0.029 0.176 ± 0.020 0.070 ± 0.013 0.084 ± 0.010 <0.001 ppb 0.339 ± 0.015 0.143 ± 0.030 0.371 ± 0.080 0.432 ± 0.060 0.580 ± 0.070 0.086 ± 0.013 0.253 ± 0.017 <0.001 ppb 0.136 ± 0.008 0.044 ± 0.007 0.070 ± 0.020 0.017 ± 0.002 <0.001 ppb 0.026 ± 0.003
0.679 ± 0.130 0.81 ± 0.15 16.56 ± 3.1 14.57 ± 3.0 1.254 ± 0.2 84.9 ± 16.3 74.3 ± 12.8 45.87 ± 8.7 54.3 ± 9.80 52.29 ± 10 55.53 ± 11 104.8 ± 19 26.36 ± 5.1 83.8 ± 14.6 616 ± 34.7 0.730 ± 0.110 0.280 ± 0.020 0.064 ± 0.020 0.141 ± 0.010 0.298 ± 0.017 0.199 ± 0.019 0.047 ± 0.013 0.045 ± 0.011 0.012 ± 0.001 0.205 ± 0.015 0.080 ± 0.012 0.248 ± 0.040 0.293 ± 0.043 0.374 ± 0.050 0.036 ± 0.003 0.200 ± 0.013 <0.001 ppb 0.029 ± 0.003 0.100 ± 0.040 0.090 ± 0.015 0.019 ± 0.002 <0.001 ppb 0.015 ± 0.001
0.760 ± 0.150 0.23 ± 0.05 33.74 ± 6.0 23.69 ± 4.2 2.80 ± 0.03 125.6 ± 25 114.8 ± 22 61.75 ± 10 25.72 ± 4.2 24.3 ± 3.61 127.6 ± 24 197 ± 32.0 46.17 ± 6.7 194 ± 33.2 978 ± 69.2 0.740 ± 0.200 0.153 ± 0.030 0.068 ± 0.013 0.090 ± 0.009 0.163 ± 0.020 0.252 ± 0.040 0.013 ± 0.001 0.740 ± 0.030 0.017 ± 0.003 0.102 ± 0.015 0.270 ± 0.050 0.780 ± 0.190 0.640 ± 0.110 0.970 ± 0.160 0.036 ± 0.005 0.600 ± 0.100 <0.001 ppb 0.320 ± 0.040 0.270 ± 0.020 0.143 ± 0.020 0.070 ± 0.009 <0.001 ppb 0.250 ± 0.030
1.09 ± 0.180 1.91 ± 0.30 47.53 ± 9.2 39.76 ± 8.2 7.08 ± 2.25 196.6 ± 39 180.5 ± 36 108.2 ± 20 23.91 ± 4.3 24.63 ± 3.8 166 ± 30.4 129 ± 25.8 99.0 ± 18.1 189.5 ± 34 1215 ± 74 0.548 ± 0.009 0.278 ± 0.020 0.028 ± 0.018 0.057 ± 0.013 0.172 ± 0.021 0.678 ± 0.120 0.393 ± 0.040 0.411 ± 0.050 0.011 ± 0.002 1.689 ± 0.040 0.137 ± 0.020 0.644 ± 0.012 1.023 ± 0.350 1.920 ± 0.400 0.010 ± 0.001 0.485 ± 0.042 <0.001 ppb 0.433 ± 0.043 0.143 ± 0.002 0.432 ± 0.060 <0.001 ppb 0.007 ± 0.003 0.056 ± 0.010
0.400 ± 0.065 0.58 ± 0.11 16.84 ± 2.3 13.62 ± 1.5 3.94 ± 0.68 106.9 ± 18 91.78 ± 15 48.69 ± 7.6 8.89 ± 1.67 7.78 ± 1.24 46.86 ± 8.2 115.5 ± 20 27.88 ± 4.4 100 ± 18.1 589.7 ± 43 0.110 ± 0.020 0.032 ± 0.006 0.016 ± 0.002 0.013 ± 0.003 0.120 ± 0.010 0.194 ± 0.015 0.136 ± 0.013 0.144 ± 0.013 0.010 ± 0.002 0.969 ± 0.170 0.068 ± 0.015 0.283 ± 0.030 0.837 ± 0.200 1.630 ± 0.300 0.057 ± 0.007 0.373 ± 0.040 <0.001 ppb 0.288 ± 0.030 0.069 ± 0.005 0.041 ± 0.005 <0.001 ppb <0.001 ppb 0.067 ± 0.007
Autumn Kings
543
1.020 ± 0.180 2.64 ± 0.50 37.35 ± 7.4 10.28 ± 1.9 2.98 ± 0.55 215.2 ± 43 177.5 ± 34 115.5 ± 22 146 ± 28 141.8 ± 28 145.82 ± 27 291.5 ± 42 66.8 ± 13.2 112.9 ± 21 1467.2 ± 89 0.017 ± 0.004 0.171 ± 0.030 0.022 ± 0.002 0.022 ± 0.003 0.280 ± 0.050 0.169 ± 0.025 0.066 ± 0.007 0.078 ± 0.009 0.058 ± 0.008 0.990 ± 0.072 0.180 ± 0.030 0.347 ± 0.060 0.342 ± 0.050 0.559 ± 0.100 0.078 ± 0.002 0.316 ± 0.019 <0.001 ppb 0.206 ± 0.009 0.135 ± 0.004 0.038 ± 0.008 0.044 ± 0.003 0.008 ± 0.002 0.010 ± 0.006 (continued on next page)
A. Zohair et al. / Chemosphere 63 (2006) 541–553
Naphthalene Acenaphthylene Acen/fluorene Phenanthrene Anthracene Fluoranthene Pyrene Benzo[a]anthracene Benzo[b]fluoranthene Benzo[k]fluoranthene Benzo[a]pyrene Indeno[1,2,3-c,d]pyrene Dibenzo[a,h]anthracene Benzo[g,h,i]perylene RPAHs PCB28 PCB52 PCB44 PCB61 PCB66 PCB101 PCB99 PCB110 PCB82 PCB118 PCB151 PCB149 PCB153 PCB138 PCB183 PCB180 PCB188 PCB170 PCB201 PCB194 PCB208 PCB205 PCB206
Carrot varieties
Cara
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Table 1 (continued) Compounds
Mean residue concentrations (lg/kg ± SD, N = 3) Potato varieties Cara
Valour
Kestrel
Desiree
Major
Nairobi
Autumn Kings
0.040 ± 0.010 6.94 ± 1.48 0.130 ± 0.033 0.150 ± 0.026 7.10 ± 1.34 6.30 ± 1.16 0.26 ± 0.04 <0.001 ppb 3.370 ± 0.570 6.600 ± 1.120 22.13 ± 4.00 0.330 ± 0.050 5.460 ± 1.070 20.43 ± 3.80 3.830 ± 0.670 2.360 ± 0.420 22.48 ± 3.70 5.400 ± 1.100 106.3 ± 13
0.032 ± 0.006 3.87 ± 0.80 0.130 ± 0.016 8.660 ± 1.400 2.300 ± 0.350 87.00 ± 16.20 1.600 ± 0.280 12.660 ± 1.900 3.970 ± 0.500 8.500 ± 1.100 177 ± 31.0 16.20 ± 2.70 13.06 ± 2.30 24.26 ± 4.10 1.06 ± 0.17 2.300 ± 0.560 44.36 ± 6.8 6.03 ± 0.83 409.1 ± 51
0.055 ± 0.004 3.56 ± 0.72 0.125 ± 0.040 0.300 ± 0.050 1.150 ± 0.170 1.640 ± 0.300 0.200 ± 0.030 0.344 ± 0.040 2.270 ± 0.360 11.730 ± 1.720 0.430 ± 0.060 31.000 ± 5.200 1.230 ± 0.210 15.100 ± 2.700 0.450 ± 0.068 1.200 ± 0.200 19.83 ± 3.10 1.830 ± 0.30 88.83 ± 12
0.236 ± 0.019 6.92 ± 1.40 0.167 ± 0.030 <0.001 ppb 7.900 ± 1.100 7.300 ± 1.200 0.300 ± 0.050 0.1 30 ± 0.026 3.500 ± 0.590 13.36 ± 2.30 18.630 ± 2.600 11.600 ± 1.890 1.830 ± 0.260 59.60 ± 7.80 18.90 ± 2.90 22.00 ± 3.20 152.4 ± 25 1.600 ± 0.210 319.2 ± 68
0.052 ± 0.008 9.607 ± 1.9 0.230 ± 0.034 0.830 ± 0.140 5.500 ± 1.100 5.000 ± 0.950 0.430 ± 0.068 1.600 ± 0.250 3.160 ± 0.570 0.570 ± 0.110 2.100 ± 0.380 22.70 ± 4.30 2.330 ± 0.410 19.56 ± 3.20 0.730 ± 0.120 1.160 ± 0.200 2.800 ± 0.530 5.600 ± 0.880 74.3 ± 8.10
0.056 ± 0.004 5.513 ± 1.1 1.215 ± 0.033 <0.001 ppb 4.330 ± 0.860 3.870 ± 0.660 1.346 ± 0.250 1.689 ± 0.280 1.098 ± 0.170 8.230 ± 1.360 2.300 ± 0.350 0.013 ± 0.002 6.770 ± 1.200 15.67 ± 2.40 <0.001 ppb 0.500 ± 0.090 2.050 ± 0.380 3.120 ± 0.560 52.2 ± 4.93
0.212 ± 0.032 4.348 ± 0.8 0.780 ± 0.130 4.260 ± 0.650 4.480 ± 1.440 8.060 ± 1.300 8.430 ± 1.200 4.300 ± 0.760 4.070 ± 0.610 2.860 ± 0.500 12.53 ± 2.10 6.100 ± 0.950 14.96 ± 1.98 127.6 ± 23 36.20 ± 6.80 34.56 ± 5.90 207.8 ± 31 1.300 ± 0.300 478.3 ± 111
A. Zohair et al. / Chemosphere 63 (2006) 541–553
PCB209 RPCBs HCB a-HCH b-HCH c-HCH Heptachlor Aldrin Heptachlor-endo-epoxide a-Endosulfan Dieldrin Endrin b-Endosulfan 4,4 0 DDE 4,4 0 ODD 2,4 0 -DDT 4,4 0 -DDT Methoxychlor ROCPs
Carrot varieties
Table 2 PAH, PCB and OCP residues in organically-farmed potatoes Compounds
Mean residue concentrations (lg/kg ± SD, N = 3) Potato varieties Cara
Kestrel
Desiree
Peel
Core
Peel
Core
Peel
Core
Peel
0.660 ± 0.132 0.310 ± 0.006 4.017 ± 0.800 3.200 ± 0.080 2.300 ± 0.360 1.210 ± 0.220 1.580 ± 0.310 0.360 ± 0.070 <0.010 ppb <0.010ppb 0.370 ± 0.060 0.372 ± 0.078 0.070 ± 0.013 0.580 ± 0.116 15.029 ± 1.264 0.139 ± 0.014 0.092 ± 0.025 0.025 ± 0.011 <0.001 ppb 0.011 ± 0.013 0.018 ± 0.002 <0.001 ppb 0.060 ± 0.009 <0.001 ppb 0.070 ± 0.030 <0.001 ppb 0.068 ± 0.030 0.116 ± 0.060 0.160 ± 0.060 <0.001 ppb 0.044 ± 0.017 <0.001 ppb <0.001 ppb 0.011 ± 0.005 0.068 ± 0.036 <0.001 ppb
0.230 ± 0.046 0.071 ± 0.014 2.850 ± 0.530 1.100 ± 0.020 0.500 ± 0.110 0.930 ± 0.176 0.880 ± 0.170 <0.01 ppb <0.01 ppb <0.01 ppb 0.169 ± 0.030 0.190 ± 0.035 0.032 ± 0.005 0.472 ± 0.090 7.423 ± 0.7662 <0.001 ppb 0.009 ± 0.003 0.004 ± 0.001 <0.001 ppb <0.001 ppb <0.001 ppb <0.001 ppb <0.001 ppb <0.001 ppb 0.030 ± 0.013 <0.001 ppb 0.010 ± 0.005 0.010 ± 0.006 0.016 ± 0.027 <0.001 ppb <0.001 ppb <0.001 ppb <0.001 ppb 0.005 ± 0.003 0.049 ± 0.010 <0.001 ppb
1.657 ± 0.320 1.366 ± 0.250 3.56 ± 0.620 3.68 ± 0.580 2.415 ± 0.430 3.48 ± 0.600 2.04 ± 0.410 0.797 ± 0.149 0.202 ± 0.040 0.201 ± 0.033 0.860 ± 0.152 0.158 ± 0.031 0.217 ± 0.034 0.697 ± 0.129 21.365 ± 1.314 0.267 ± 0.100 0.160 ± 0.050 <0.001 ppb 0.027 ± 0.006 0.064 ± 0.020 0.059 ± 0.018 0.009 ± 0.002 0.008 ± 0.002 <0.001 ppb 0.043 ± 0.019 0.020 ± 0.010 0.122 ± 0.050 0.096 ± 0.033 0.067 ± 0.023 0.015 ± 0.006 0.021 ± 0.006 <0.001 ppb 0.013 ± 0.005 <0.001 ppb 0.005 ± 0.002 <0.001 ppb
1.525 ± 0.300 <0.01 ppb 2.800 ± 0.450 2.780 ± 0.460 0.915 ± 0.163 1.750 ± 0.350 1.080 ± 0.210 0.240 ± 0.047 0.060 ± 0.012 0.142 ± 0.026 0.459 ± 0.081 0.109 ± 0.020 0.059 ± 0.011 0.395 ± 0.075 12.314 ± 0.984 0.030 ± 0.013 0.010 ± 0.001 <0.001 ppb <0.001 ppb 0.019 ± 0.007 0.018 ± 0.007 <0.001 ppb 0.003 ± 0.001 <0.001 ppb 0.011 ± 0.004 0.006 ± 0.002 0.014 ± 0.006 0.010 ± 0.005 0.008 ± 0.003 <0.001 ppb <0.001 ppb <0.001 ppb <0.001 ppb <0.001 ppb <0.001 ppb <0.001 ppb
0.053 ± 0.010 0.035 ± 0.006 1.230 ± 0.236 1.460 ± 0.250 0.074 ± 0.014 1.340 ± 0.240 1.210 ± 0.220 0.450 ± 0.085 <0.01 ppb <0.01 ppb <0.01 ppb <0.01 ppb <0.01 ppb <0.01 ppb 5.852 ± 0.599 0.314 ± 0.060 0.200 ± 0.050 0.030 ± 0.006 0.046 ± 0.007 0.165 ± 0.060 0.056 ± 0.120 0.010 ± 0.009 0.015 ± 0.001 <0.001 ppb 0.039 ± 0.012 0.013 ± 0.001 0.053 ± 0.020 0.041 ± 0.016 0.042 ± 0.015 0.006 ± 0.002 0.023 ± 0.001 <0.001 ppb 0.009 ± 0.060 0.013 ± 0.004 0.011 ± 0.005 <0.001 ppb
<0.01 ppb <0.01 ppb 0.370 ± 0.070 0.610 ± 0.090 <0.01 ppb 1.070 ± 0.214 0.490 ± 0.095 0.025 ± 0.004 <0.01 ppb <0.01 ppb <0.01 ppb <0.01 ppb <0.01 ppb <0.01 ppb 2.565 ± 0.331 0.180 ± 0.050 0.071 ± 0.020 0.021 ± 0.007 0.024 ± 0.005 0.078 ± 0.020 0.005 ± 0.001 0.004 ± 0.001 0.004 ± 0.001 <0.001 ppb 0.010 ± 0.002 0.009 ± 0.002 0.004 ± 0.001 0.010 ± 0.003 0.011 ± 0.003 <0.001 ppb <0.001 ppb <0.001 ppb <0.001 ppb <0.001 ppb 0.005 ± 0.001 <0.001 ppb
0.100 ± 0.012 <0.01 ppb 6.240 ± 2.100 4.960 ± 0.670 1.126 ± 0.320 4.600 ± 1.650 1.710 ± 0.330 0.480 ± 0.090 <0.01 ppb <0.01 ppb 0.055 ± 0.010 0.184 ± 0.030 0.730 ± 0.220 0.422 ± 0.110 20.607 ± 2.189 0.250 ± 0.080 0.080 ± 0.004 0.028 ± 0.008 0.050 ± 0.008 0.095 ± 0.021 0.122 ± 0.030 <0.001 ppb 0.026 ± 0.010 <0.001 ppb 0.054 ± 0.015 0.078 ± 0.030 0.330 ± 0.090 0.310 ± 0.130 0.217 ± 0.060 0.007 ± 0.001 0.105 ± 0.030 <0.001 ppb <0.001 ppb 0.014 ± 0.005 0.012 ± 0.004 <0.001 ppb
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0.042 ± 0.010 <0.01 ppb 3.600 ± 0.860 3.320 ± 0.580 0.158 ± 0.280 2.320 ± 0.410 0.600 ± 0.070 0.370 ± 0.120 <0.01 ppb <0.01 ppb <0.01 ppb <0.01 ppb 0.022 ± 0.006 0.114 ± 0.020 10.546 ± 1.300 0.137 ± 0.040 0.063 ± 0.020 0.016 ± 0.008 <0.001 ppb 0.030 ± 0.005 0.080 ± 0.020 <0.001 ppb 0.011 ± 0.005 <0.001 ppb 0.010 ± 0.004 0.024 ± 0.006 0.190 ± 0.040 0.150 ± 0.030 0.130 ± 0.030 <0.001 ppb 0.050 ± 0.014 <0.001 ppb <0.001 ppb 0.007 ± 0.004 0.006 ± 0.003 <0.001 ppb (continued on next page)
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Naphthalene Acenaphthylene Acen/Fluorene Phenanthrene Anthracene Fluoranthene Pyrene Benzo[a]anthracene Benzo[b]fluoranthene Benzo[k]fluoranthene Benzo[a]pyrene Indeno[1,2,3-c,d]pyrene Dibenzo[a,h]anthracene Benzo[g,h,i]perylene RPAHs PCB28 PCB52 PCB44 PCB61 PCB66 PCB101 PCB99 PCB110 PCB82 PCB118 PCB151 PCB149 PCB153 PCB138 PCB183 PCB180 PCB188 PCB170 PCB201 PCB194 PCB208
Valour
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Table 2 (continued) Compounds
Mean residue concentrations (lg/kg ± SD, N = 3) Potato varieties Cara
Kestrel
Desiree
Peel
Core
Peel
Core
Peel
Core
Peel
Core
<0.001 ppb <0.001 ppb 0.027 ± 0.010 0.909 ± 0.223 <0.001 ppb <0.001 ppb <0.001 ppb 0.560 ± 0.112 <0.001 ppb <0.001 ppb 1.230 ± 0.240 3.230 ± 0.460 0.860 ± 0.170 <0.001 ppb <0.001 ppb 1.460 ± 0.290 0.067 ± 0.012 <0.001 ppb 0.160 ± 0.030 0.300 ± 0.050 7.867 ± 0.965
<0.001 ppb <0.001 ppb <0.001 ppb 0.133 ± 0.041 <0.001 ppb <0.001 ppb <0.001 ppb 0.100 ± 0.018 <0.001 ppb <0.001 ppb <0.001 ppb 1.930 ± 0.380 <0.001 ppb <0.001 ppb <0.001 ppb 0.460 ± 0.062 <0.001 ppb <0.001 ppb <0.001 ppb <0.001 ppb 2.49 ± 0.538
<0.001 ppb <0.001 ppb <0.001 ppb 0.996 ± 0.237 <0.001 ppb <0.001 ppb <0.001 ppb 3.660 ± 0.630 0.430 ± 0.070 <0.001 ppb 1.900 ± 0.300 <0.001 ppb 24.000 ± 3.900 10.860 ± 1.870 2.130 ± 0.320 13.130 ± 2.100 0.330 ± 0.055 0.266 ± 0.030 3.670 ± 0.400 4.130 ± 0.720 64.506 ± 7.720
<0.001 ppb <0.001 ppb <0.001 ppb 0.129 ± 0.036 <0.001 ppb <0.001 ppb <0.001 ppb 0.330 ± 0.040 0.300 ± 0.040 <0.001 ppb <0.001 ppb <0.001 ppb 14.800 ± 2.320 5.460 ± 1.000 <0.001 ppb 0.230 ± 0.040 <0.001 ppb <0.001 ppb 0.430 ± 0.080 2.300 ± 0.370 23.85 ± 4.188
<0.001 ppb 0.008 ± 0.003 <0.001 ppb 1.094 ± 0.245 <0.001 ppb <0.001 ppb 0.270 ± 0.035 0.159 ± 0.025 0.067 ± 0.010 0.119 ± 0.020 0.830 ± 0.120 2.500 ± 0.330 0.088 ± 0.013 13.300 ± 2.100 0.023 ± 0.003 1.430 ± 0.230 0.012 ± 0.002 0.330 ± 0.060 1.330 ± 0.220 0.600 ± 0.100 21.058 ± 3.649
<0.001 ppb <0.001 ppb <0.001 ppb 0.436 ± 0.115 <0.001 ppb <0.001 ppb <0.001 ppb <0.001 ppb <0.001 ppb 0.019 ± 0.003 0.370 ± 0.050 0.042 ± 0.006 0.015 ± 0.003 4.900 ± 0.700 <0.001 ppb 0.100 ± 0.016 <0.001 ppb <0.001 ppb 0.260 ± 0.050 <0.001 ppb 5.706 ± 1.347
<0.001 ppb <0.001 ppb <0.001 ppb 1.778 ± 0.417 0.033 ± 0.004 <0.001 ppb 0.960 ± 0.180 1.070 ± 0.200 0.026 ± 0.003 <0.001 ppb 1.100 ± 0.230 2.100 ± 0.310 12.200 ± 2.500 0.167 ± 0.034 1.530 ± 0.250 12.430 ± 2.430 1.930 ± 0.260 1.930 ± 0.280 13.900 ± 2.500 1.070 ± 0.180 50.446 ± 8.543
<0.001 ppb <0.001 ppb <0.001 ppb 0.904 ± 0.225 <0.001 ppb <0.001 ppb <0.001 ppb 0.570 ± 0.100 <0.001 ppb <0.001 ppb <0.001 ppb 0.026 ± 0.003 1.630 ± 0.240 0.006 ± 0.002 <0.001 ppb 0.167 ± 0.032 <0.001 ppb <0.001 ppb 1.820 ± 0.270 0.330 ± 0.036 4.549 ± 0.674
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PCB205 PCB206 PCB209 RPCBs HCB a-HCH b-HCH c-HCH Heptachlor Aldrin Heptachlor-endo-epoxide a-Endosulfan Dieldrin Endrin b-Endosulfan 4,4 0 DDE 4,4 0 DDD 2,4 0 -DDT 4,4 0 -DDT Methoxychlor ROCPs
Valour
Table 3 PAH, PCB and OCP residues in organically-farmed carrots Compounds
Mean residue concentrations (lg/kg ± SD, N = 3) Carrot varieties Major
Autumn Kings
Core
Peel
Core
Peel
0.137 ± 0.028 0.060 ± 0.013 1.436 ± 0.190 1.270 ± 0.180 1.470 ± 0.210 5.430 ± 1.230 2.543 ± 0.720 0.673 ± 0.220 0.270 ± 0.070 0.278 ± 0.030 0.530 ± 0.015 0.229 ± 0.010 1.100 ± 0.190 0.550 ± 0.012 14.976 ± 1.415 0.300 ± 0.120 0.055 ± 0.020 0.019 ± 0.005 0.032 ± 0.012 0.070 ± 0.028 0.154 ± 0.060 0.006 ± 0.013 0.077 ± 0.009 <0.001 ppb 0.176 ± 0.030 0.018 ± 0.005 0.131 ± 0.011 0.076 ± 0.008 0.291 ± 0.100 <0.001 ppb 0.032 ± 0.006 <0.001 ppb 0.041 ± 0.014 0.081 ± 0.025 0.232 ± 0.008 <0.001 ppb <0.001 ppb
0.051 ± 0.009 0.018 ± 0.004 0.480 ± 0.100 0.860 ± 0.260 0.757 ± 0.200 1.153 ± 0.180 0.095 ± 0.016 0.053 ± 0.011 0.093 ± 0.015 0.094 ± 0.015 0.134 ± 0.010 0.079 ± 0.012 <0.01 ppb 0.072 ± 0.013 3.938 ± 0.375 0.230 ± 0.090 0.015 ± 0.004 0.008 ± 0.002 0.0153 ± 0.006 0.020 ± 0.007 0.021 ± 0.006 <0.001 ppb <0.001 ppb <0.001 ppb <0.001 ppb <0.001 ppb <0.001 ppb <0.001 ppb 0.024 ± 0.005 <0.001 ppb 0.020 ± 0.003 <0.001 ppb <0.001 ppb 0.006 ± 0.002 0.066 ± 0.014 <0.001 ppb <0.001 ppb
0.036 ± 0.005 0.027 ± 0.005 1.030 ± 0.210 1.064 ± 0.280 1.850 ± 0.320 9.826 ± 1.690 <0.01 ppb 0.296 ± 0.049 0.424 ± 0.074 0.400 ± 0.070 0.310 ± 0.062 0.193 ± 0.028 0.169 ± 0.030 0.386 ± 0.070 16.011 ± 2.551 0.070 ± 0.013 0.013 ± 0.004 0.010 ± 0.003 <0.001 ppb 0.076 ± 0.021 0.060 ± 0.018 0.024 ± 0.006 0.034 ± 0.013 <0.001 ppb 0.100 ± 0.004 <0.001 ppb 0.070 ± 0.030 0.154 ± 0.045 0.280 ± 0.007 <0.001 ppb 0.035 ± 0.005 <0.001 ppb 0.014 ± 0.003 <0.001 ppb 0.008 ± 0.002 <0.001 ppb <0.001 ppb
0.012 ± 0.002 <0.01 ppb 0.520 ± 0.100 0.438 ± 0.860 0.612 ± 0.120 2.926 ± 0.480 <0.01 ppb 0.045 ± 0.009 0.168 ± 0.030 0.167 ± 0.028 0.1 88 ± 0.035 <0.01 ppb <0.01 ppb <0.01 ppb 5.076 ± 0.767 0.034 ± 0.011 0.006 ± 0.002 <0.001 ppb <0.001 ppb 0.039 ± 0.006 0.005 ± 0.003 <0.001 ppb 0.004 ± 0.001 <0.001 ppb 0.025 ± 0.005 <0.001 ppb 0.006 ± 0.002 0.005 ± 0.001 0.017 ± 0.005 <0.001 ppb <0.001 ppb <0.001 ppb <0.001 ppb <0.001 ppb 0.003 ± 0.001 <0.001 ppb <0.001 ppb
0.673 ± 0.130 1.135 ± 0.227 3.120 ± 0.620 1.690 ± 0.200 0.913 ± 0.180 16.530 ± 3.100 1.1660 ± 0.233 0.875 ± 0.175 1.290 ± 0.256 1.194 ± 0.218 1.900 ± 0.350 0.800 ± 0.140 0.476 ± 0.090 0.510 ± 0.100 32.272 ± 4.151 0.006 ± 0.002 0.018 ± 0.002 0.015 ± 0.003 0.005 ± 0.002 0.120 ± 0.019 0.043 ± 0.012 0.004 ± 0.001 0.046 ± 0.013 0.007 ± 0.003 0.010 ± 0.002 0.009 ± 0.004 0.090 ± 0.013 0.070 ± 0.021 0.109 ± 0.030 0.018 ± 0.004 0.029 ± 0.006 <0.001 ppb 0.047 ± 0.008 0.008 ± 0.003 <0.001 ppb <0.001 ppb <0.001 ppb
Core 0.550 ± 0.120 <0.01 ppb 1.540 ± 0.440 0.880 ± 0.160 0.520 ± 0.130 2.940 ± 0.580 0.166 ± 0.032 <0.01 ppb 0.212 ± 0.040 0.187 ± 0.034 0.588 ± 0.115 0.148 ± 0.027 0.072 ± 0.014 0.041 ± 0.008 7.804 ± 0.806 <0.001 ppb 0.013 ± 0.005 <0.001 ppb <0.001 ppb 0.050 ± 0.006 0.022 ± 0.004 <0.001 ppb 0.005 ± 0.002 <0.001 ppb 0.003 ± 0.001 <0.001 ppb 0.010 ± 0.003 0.010 ± 0.002 0.030 ± 0.004 <0.001 ppb <0.001 ppb <0.001 ppb 0.006 ± 0.002 0.003 ± 0.001 <0.001 ppb <0.001 ppb <0.001 ppb (continued on next page)
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Peel
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Naphthalene Acenaphthylene Acen/Fluorene Phenanthrene Anthracene Fluoranthene Pyrene Benzo[a]anthracene Benzo[b]fluoranthene Benzo[k]fluoranthene Benzo[a]pyrene Indeno[1,2,3-c,d]pyrene Dibenzo[a,h]anthracene Benzo[g,h,i]perylene RPAHs PCB28 PCB52 PCB44 PCB61 PCB66 PCB101 PCB99 PCB110 PCB82 PCB118 PCB151 PCB149 PCB153 PCB138 PCB183 PCB180 PCB188 PCB170 PCB201 PCB194 PCB208 PCB205
Nairobi
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Table 3 (continued) Compounds
Mean residue concentrations (lg/kg ± SD, N = 3) Carrot varieties
PCB206 PCB209 RPCBs HCB a-HCH b-HCH c-HCH Heptachlor Aldrin Heptachlor-endo-epoxide a-Endosulfan Dieldrin Endrin b-Endosulfan 4,4 0 DDE 4,4 0 DDD 2,4 0 -DDT 4,4 0 -DDT Methoxychlor ROCPs
Nairobi
Autumn Kings
Peel
Core
Peel
Core
Peel
Core
0.007 ± 0.002 0.007 ± 0.003 1.805 ± 0.393 0.100 ± 0.020 0.200 ± 0.037 <0.001 ppb <0.001 ppb 0.200 ± 0.030 0.140 ± 0.023 1.930 ± 0.350 0.030 ± 0.005 1.300 ± 0.210 7.320 ± 1.400 0.009 ± 0.002 0.860 ± 0.140 0.100 ± 0.019 0.280 ± 0.048 1.300 ± 0.240 2.700 ± 0.440 16.469 ± 2.081
<0.001 ppb <0.001 ppb 0.425 ± 0.132 0.050 ± 0.010 0.100 ± 0.019 <0.001 ppb <0.001 ppb <0.001 ppb 0.013 ± 0.002 1.020 ± 0.017 <0.001 ppb 0.030 ± 0.004 3.400 ± 0.650 0.006 ± 0.001 0.017 ± 0.003 0.010 ± 0.002 0.150 ± 0.030 0.900 ± 0.150 <0.001 ppb 5.696 ± 0.969
<0.001 ppb <0.001 ppb 0.948 ± 0.238 0.260 ± 0.035 <0.001 ppb 2.070 ± 0.038 0.230 ± 0.034 0.200 ± 0.036 0.270 ± 0.500 0.490 ± 0.078 <0.001 ppb 1.760 ± 0.300 0.006 ± 0.001 0.009 ± 0.003 0.500 ± 0.120 <0.001 ppb 0.350 ± 0.050 0.520 ± 0.110 0.240 ± 0.045 6.905 ± 0.714
<0.001 ppb <0.001 ppb 0.144 ± 0.041 0.140 ± 0.018 < 0.001 ppb 0.330 ± 0.053 0.150 ± 0.030 0.027 ± 0.005 0.125 ± 0.023 0.021 ± 0.004 <0.001 ppb 0.100 ± 0.020 <0.001 ppb 0.004 ± 0.001 <0.001 ppb <0.001 ppb 0.180 ± 0.036 0.110 ± 0.022 <0.001 ppb 1.187 ± 0.113
<0.001 ppb 0.020 ± 0.005 0.674 ± 0.147 0.330 ± 0.053 2.860 ± 0.520 <0.001 ppb 5.100 ± 1.030 5.050 ± 0.900 2.900 ± 0.480 1.670 ± 0.330 1.270 ± 0.230 2.900 ± 0.470 0.590 ± 0.120 6.160 ± 0.960 36.600 ± 6.300 3.830 ± 0.660 8.000 ± 1.400 47.760 ± 9.200 0.730 ± 0.140 125.750 ± 26.070
<0.001 ppb <0.001 ppb 0.152 ± 0.044 0.036 ± 0.006 0.100 ± 0.020 <0.001 ppb 0.400 ± 0.070 <0.001 ppb 0.660 ± 0.120 0.560 ± 0.110 0.200 ± 0.032 0.900 ± 0.150 <0.001 ppb <0.001 ppb 1.360 ± 0.240 0.700 ± 0.130 0.330 ± 0.630 1.600 ± 0.320 0.430 ± 0.080 7.276 ± 1.106
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Major
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and extracted for 24 h with 300 ml of hexane:acetone (1:1). Extracts were then reduced to near dryness on a rotary film evaporator (Buchi R-124), taken up in 10 ml hexane and transferred into pre-washed and baked glass vials. The samples were then reduced farther on a Techne Dri-Block under a gentle stream of N2 to 2 ml. The extracts were cleaned by passing through Bakerbond PCB-A SPE cartridges pre-conditioned with 10 ml hexane. They were again reduced under N2 to near dryness, transferred to clean glass vials and made up to 1 ml for analysis. One microlitre of each clean sample extract was injected into an Hewlett Packard 6890 gas chromatograph fitted with a 30 m HP5-MS fused silica capillary column (30 · 0.25 mm · 0.25 lm film thickness) and connected to an Hewlett Packard 5973 mass selective detector. The carrier gas was helium, maintained at a flow rate of 1.0 ml/min by electronic pneumatic control. The injection port temperature was 230 C with electron energy of 70 eV. The quadrupole temperature was 280 C. The instrument was tuned on PFTBA. The oven programme for all three classes of compounds was as follows: 100 C for 2 min, 5 C/min to 200 C for 6 min, 4 C/min to 280 C for 7 min, 90 C for 2 min, 10 C/min to 240 C, 3 C/min to 310 C for 5 min and 100 C for 2 min, 5 C/min to 200 C for 6 min, 4 C/min to 280 C for 2 min, respectively. Calibration was by seven external standards over the concentration ranges l–30 ng/ml for PCBs, 1– 1000 ng/ml for PAHs and 1–100 ng/ml for OCPs. The mass spectrometer was operated in selective ion monitoring mode using separate ions to identify and confirm compounds.
3. Results and discussion A multi-analytical method was developed for the analysis of PAHs, PCBs and OCPs in the same extract of plant and soil samples. Recoveries for surrogate D-PAHs in plant and soil ranged between 84% and 111% and between 90% and 115%, respectively, with low RSD% ranging from 3 to 12. Slightly lower recoveries (69–78%) of low molecular weight naphthalene were likely due to losses occurring during extraction and clean-up; this is typically reported (WHO, 1998). Mean recoveries of the 13C surrogate PCBs from soils ranged from 92% to 124% with RSD% ranging from 4 to 19. Mean recoveries of surrogate OCPs from plants and soils fell in the range 80–108% and 83–112%, respectively, with low RSD% ranging from 3 to 14. Such recoveries were in a similar range to those frequently reported for these three classes of compounds therefore we considered our own method to be reliable. Table 1 shows the PAH concentrations of the soils in which the organic potatoes and carrots investigated were grown. The most abundant individual PAH compound
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in soil investigated here was indeno[1,2,3-c,d]pyrene. Benzo[a]pyrene, fluoranthene, pyrene, benzo[a]anthracene and benzo[g,h,i]perylene were also relatively abundant reflecting their lower water solubility and lower vapour pressures. The soils RPAHs concentrations ranged from 590 ± 43 to 2301 ± 146 lg/kg. In both the peels and the cores of different potato varieties, the PAH burden was dominated by the low molecular weight compounds acenapthene/fluorine ranging from 1.6 ± 0.3 to 9.84 ± 2.9 lg/kg and phenanthrene in the range 2.07 ± 0.3 to 8.28 ± 1.3 lg/kg (Table 2). These compounds are more water-soluble and more volatile than the relatively high molecular weight PAHs, which were more abundant in soils (Table 1), therefore it is not surprising that they were more susceptible to crop uptake. The potatoes also contained relatively high amounts of fluoranthene and pyrene, reflecting their relatively high concentration in the crop-associated soils. The results in Table 3 also show that fluoranthene, ranging from 6.58 ± 1.4 to 19.5 ± 3.6 lg/kg, is the most abundant individual PAH compound detected in carrots. The concentrations of RPAHs in organic carrots ranged from 18.9 ± 0.79 to 40.1 ± 4.9 lg/kg and from 8.4 ± 0.93 to 33.7 ± 2.30 lg/kg in organic potatoes— markedly higher than the PAH concentrations in potatoes grown in conventional farms reported by Ladovici et al. (1995), Kazerouni et al. (2001) and Vikelsoe et al. (2002). However, in comparison to two studies in China the contaminant concentrations reported here were relatively low. Tao et al. (2004) reported that almost all 16 U.S.EPA-listed PAHs were found in root crops and that concentrations were 72 ng/g in a lesser contaminated area compared to 210 ng/g in root crops grown in soils close to an urban area and irrigated with wastewater. Amongst the PCBs, congener 138 was the most abundant in all tested samples except Kestrel potatoes and Autumn King carrots where congeners 28 and 118 were the highest, respectively. The results are in agreement with those reported by Theobald (2003) who found that PCB 138 was the most abundant congener in soils that they investigated. Organic vegetables investigated contained PCB levels ranging from 0.83 ± 0.19 to 2.68 ± 0.94 lg/kg, however, such levels do not give cause for concern in relation to the maximum UK tolerable daily intake limit of 10 pg/kg/body weight/day (Tao et al., 2004). Although organic farming avoids the use of pesticides, residues may remain from pre-organic farming applications or as a result of atmospheric deposition. DDT, endrin, c-HCH (lindane) and endosulfan were the most frequently detected OCPs in soils investigated here (Table 1). From Tables 2 and 3 it is evident that these OCP residues may transfer to crops, however, the levels detected were below the maximum residue limits (MRLs) of FAO/WHO (1993). Crop uptake of HCB was relatively low (<0.0010.037 lg/kg) in all tested
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samples but DDT levels ranged from 3.6 to 100 lg/kg, which might give cause for concern. Aldrin is converted to dieldrin by an epoxidation process in biological system (Rumsey and Bond, 1974) and therefore dieldrin is expected to be found in relatively higher concentrations than aldrin as we found in this study (Tables 1–3). There was a significant positive correlation (P < 0.05) between concentrations of PCBs and OCPs in soil and their uptake by carrots (Fig. 1) but no correlation was observed for PAHs with carrots or any of the compounds with any potato variety. This suggests that characteristics of the chemicals and the crop species were most important in determining uptake. Chiou et al. (2001) reported that plant lipids is the major factor causing observed differences in plant uptake of lipophilic contaminants such as aldrin, dieldrin, heptachlor and heptachlor-epoxide. Stronger correlations for carrots than potatoes may be explained by the presence of oil channels in carrots as previously suggested by WHO (1998) and Kipopoulou et al. (1999). Significant positive correlations (P < 0.05) were found between varieties and uptake; Desiree potato variety and Nairobi carrot variety were more susceptible to PAH contamination while Kestrel potato variety had high ability to uptake PCBs
and OCPs from contaminated soils. Gao and Zhu (2004) found that uptake, accumulation and translocation of phenanthrene and pyrene by 12 plant species grown in soils treated by different concentrations of phenanthrene and pyrene were correlated with their soil concentrations and also dependent on plant species. Characteristics of crop species that influence contaminant uptake is worthy of more detailed investigation. Soil–crop bioconcentration factors (BCFs) decreased with increasing log Kow for PAHs up to about 4.5 and for PCBs up to about 6.5, above which no changes were observed for either class of contaminants (Fig. 2). No relationship was observed between soil–crop BCFs and log Kow for OCPs, most likely because their concentrations were low and variable. In addition to characteristics of crops and physico-chemical properties of the chemical residues, soil–plant transfer of persistent organic chemical residues will depend on the physical and chemical characteristics of the soils in which they are grown. Organic matter content and moisture content are the soil factors most frequently reported to exert the greatest impact on availability of soil-sorbed nonionic organic chemical residues to uptake by crops (Beck et al., 1996). Generally, crop uptake would be favoured under
Fig. 1. Correlation between the concentrations of PCBs and OCPs in carrots and soils in which they were grown.
Fig. 2. Relationship between the crop:soil BCFs of PAHs and PCBs with their log Kow in Autumn King carrots (pyramids) and Valour potatoes (spheres). BCF = (P + C)/S = contaminant concentrations in peel + contaminant concentrations in core/contaminant concentrations in soils.
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moist conditions in soils with low organic matter contents whereas in dry soils with high organic matter contents the chemical residues will be strongly bound by the soil retarding uptake. In this study the soil organic
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matter content ranged from 3% to 5% so they have been a factor in explaining the differences observed. Soil pH ranged from 6.5 to 7.6 but was not considered important given that the chemicals investigated are nonionic or only
Fig. 3. Comparison between the concentrations of PAHs, PCBs and OCPs in the peels and cores of carrots and potatoes.
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weakly ionic. Effectively, all of the aforementioned factors will combine in complex ways to control the uptake of the chemicals from the soils into the carrots and potatoes, however, caution needs to be exercised in considering the assertions made here because even where statistically significant differences were observed between crop residue concentrations it was impossible to ascertain the main factors responsible for these differences due to the limited number of samples available. From Fig. 3 it can be seen that PAHs, PCBs and OCPs are all much more abundant in the peels of both potatoes and carrots. This observation has been made by many researchers including OÕConnor et al. (1990); WHO (1998) and Wild and Jones (1992). Greater lipid content in potato peels than that in their corresponding cores were attributed by Chiou et al. (2001) and Fismes et al. (2002) to the higher lipid contents of the peels. Removal of organic pollutant residues from potato and carrot varieties after peeling ranged from 55.9% to 100%, 52% to 100% and 57.5% to 100% for PAHs, PCBs and OCPs, respectively. The potential for peel to core translocation depended on plant variety. For example, lowest PCBs removal by peeling was observed for Desiree potatoes (55.9–67.7%). This likely reflects the higher dry matter content of Desiree potatoes than any other crop investigated.
4. Concluding remarks Our results show that PAHs, PCBs and OCPs were taken up by carrots and potatoes from soils. Uptake depended on crop varieties but more research is needed to establish whether this was related to characteristics of the crops or if it was simply a reflection of spatial variability in the distribution of contaminant residues in the soils in which the different crops were grown. Both factors likely contributed because we observed that all contaminants were more abundant in the peels than the cores of all crop varieties reflecting higher peel lipid contents, and because PCB and OCP concentrations in crops were strongly correlated with their concentrations in associated soils. Most of the compounds considered here have been reported to have endocrine disrupting properties, and some are known or suspected carcinogens. Thus, their presence in food is of concern and intakes should be as low as reasonably practicable (COT, 1996). Food containing residues at or below the respective MRLs are considered to be toxicologically acceptable for long-term intake (White et al., 2002). On this basis, the concentrations of contaminant residues in the organic vegetables analysed here should not give cause for concern, however, it is possible that even such low levels of contaminants may merit more detailed scrutiny in the near future. For example, Pesticides Safety Directorate, 2001 and Codex Committee on
Pesticide Residue, 2001 have stated that the need for an Acute Reference Dose (ARfD) will be considered for all pesticides in the future, and the estimated short-term intake of pesticide residues will be compared with the ARfDs in order to interpret the possible risks associated with unit-to-unit, e.g. carrot to carrot, variability in residue levels (Renwick et al., 2003). Despite the complexity of risk assessment procedures and generally slow development and introduction of legislation in EU and elsewhere that will require their use in hazard assessment and human exposure management, it is clear that relatively simple procedures such as peeling root crops like carrots and potatoes can considerably reduce exposure. The more urgent need is for efforts to ensure that the general public are better informed about the risks from contaminants in foodstuffs and, in particular, how they can reduce their personal exposure by simple procedures such as adequate washing and peeling. This is particularly true with respects to environmental contaminants in organically-farmed vegetables where much of the public may be misinformed with regards to the relative safety of such products as compared to their conventionally-farmed counterparts. However, it should be stressed that the levels POPs in vegetables are low and can be reduced further by appropriate preparation and cooking. The risks to health that they may present are outweighed by the nutritional benefits of a healthy balanced diet including the recommended consumption of 5 portions of fruit and vegetables each day.
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