Fs

Chemosphere,Vol.39, No. 3, pp.419-429, 1999

Pergamon

© 1999ElsevierScienceLtd.All rightsreserved 0045-6535/99/$ - see frontmatter

PII: S0045-6535(99)00005-3

S O I L M O N I T O R I N G IN T H E V I C I N I T Y O F A M U N I C I P A L S O L I D W A S T E INCINERATOR: TEMPORAL VARIATION OF PCDD/Fs

M. Schuhmacher', J.L. Domingo2, S. Granero2, J.M Llobet2, E. Eljarrat 3 and J. Rivera3

1Environmental Engineering Laboratory, "Rovira i Virgili" University, 43007 Tarragona, Spain 2Laboratory of Toxicology and Environmental Health, "Rovira i Virgili" University, San Lorenzo 21, 43201 Reus, Spain 3Mass Spectroscopy Laboratory, C.L D, CSIC, Barcelona, Spain (Receivedin Germany15June1998;accepted3 December1998) ABSTRACT

To determine the temporal variation in the levels of polychlorinated dibenzo-p-dioxins (PCDDs) and dibenzofurans (PCDFs) in soils in the vicinity of a municipal solid waste incinerator (MSWI), 24 soil samples were collected at the same points in which samples had been taken one year before. In the previous survey, PCDD/F concentrations ranged from 0.22 to 5.80 ng I-TEQ/kg (dry matter) with median and mean values of 0.80 and 1.08 ng I-TEQ/kg (dry matter), respectively. In the present survey, PCDD/F levels ranged from 0.11 to 3.88 ng I-TEQ/kg (dry matter) with a median value of 0.88 ng I-TEQ/kg (dry matter) and a mean value of 1.17 ng I-TEQ/kg (dry matter). It means an increase of 8.3% in the mean PCDD/F levels during the last year. In turn, the mean PCDD/PCDF ratios were 0.62 (previous survey) and 0.55 (current survey), respectively. A comparison of the increases in the quantities of PCDD/Fs found in soils with those estimated according calculations suggests that no remarkable sources of PCDD/F emissions other than the MSWI are present in the area here examined. The differences between the current results and those found in 1996 could be explained by the heterogeneity of the samples. ©1999ElsevierScienceLtd. All rightsreserved

Key-words: PCDD, PCDF, soils, temporal variation, municipal solid waste incinerator, Tarragona (Spain).

419

420 INTRODUCTION

Incineration of municipal, biomedical and hazardous waste is one of the most used options to reduce and to destroy substances that pose a risk to human health [1]. However, the emissions of a full range of inorganic and organic compounds have become one of the most controversial issues in siting and building new incinerators. In relation to municipal solid waste (MSW) incineration, typical air contaminants of concern are metals and polychlorinated dibenzo-p-dioxins (PCDDs) and dibenzofurans (PCDFs). Because of their great toxicity and potential carcinogenicity, PCDD/Fs are the chemical compounds of greatest concern for MSW incinerators [2-4]. PCDDs and PCDFs, especially the 2,3,7,8-substituted congeners, belong to the most hazardous environmental contaminants. They are generated and released in the environment primarily as byproducts of chemical manufacturing processes such as chlorophenols and some chlorinated herbicides, and during combustion of municipal and chemical wastes [5-9]. PCDD/Fs were detected in emissions from MSW incinerators in 1977 [10] and are present in all environmental compartments (air, soils, sediments, vegetation and water). Moreover, given the persistent nature and relative immobility of these compounds, terrestrial and aquatic organisms are also liable to exposure [11-12]. The emission of trace amounts of metals and PCDD/Fs together with other products of incineration has raised concern about the health and environmental consequences of this process [13]. The lack of comprehensive evaluations of the PCDD/F formation and emission control technologies in earlier times resulted in ambiguity in the decision-making of incineration projects [14]. Therefore, in recem years a number of measures for reduction of emission products of incinerators have been adopted. Recently, the concentrations of metals and PCDD/Fs were determined in soil and vegetation samples collected near a MSW incinerator fromTarragona (Catalonia, Spain) [15-17]. In this plant, an acid gas (HC1/SO2) and metal emission limit equipment, which can complement the control of PCDD/F emissions, has been just installed. While acid gas sorbents may reduce PCDD/F formation rates, the use of activated carbon for the control of mercury emissions can also reduce PCDD/F emissions. The efficacy of the new equipment on the atmospheric emissions of metals and PCDD/Fs will be assessed in the near future. In order to establish this efficacy, the knowledge of the temporal variation in the environmental levels of PCDD/Fs in the area under potential influence of the plant should be of great interest. To assess the temporal variation in the levels of PCDD/Fs in soil and vegetation in the vicinity of the facility, in 1996 and again in 1997, soil and herbage samples were collected and PCDD/F concentrations were determined. Because PCDD/F emissions from MSW incinerators result in subsequent aerial deposition onto soil, plants, and water [18], in the current monitoring program soil and vegetation samples are being used. Since vegetation is probably more adequate than soil to bring information on the short-term exposure to PCDD/Fs, the temporal variation in the levels of these organic pollutants in herbage samples was recently assessed [ 19]. Although soil is an accumulating matrix that is useful rather to describe a long-tern exposure to PCDD/Fs, the

421 knowledge of PCDD/F concentrations in soils can be also of interest as an additional information to determine the general trend of these compounds in the area under evaluation. Consequently, PCDD/F levels in soil samples are presented here and compared with those obtained in the 1996 survey.

EXPERIMENTAL

Sampling

In June 1997, 24 soil samples were collected in the same points in which samples had been also taken in the 1996 study [16]. A wide description of the facility and surroundings, the prevailing winds in the area, and the characteristics of soils were previously reported [16]. Duplicate soil samples were collected at 250, 500, 750, 1000, 1250 and 1500 m from the stack in each of the four main directions of the wind rose in the area (NE, NW, SE, SW).

Chemical analysis

Homogenized soil samples were dried and sieved (2 mm mesh). Samples were subsequently transferred into a soxhlet apparatus and spiked with 1 ng of each of 10 different ~3C-labelledPCDD/F standards, corresponding to the tetra- to octochloro homologues (Wellington Laboratories, Guelph, Canada). After extraction with toluene for 48 h, the extracts were evaporated to 2 ml. The clean-up was carried out using a three column disposable set: multilayer silica colunm, florisil, and basic alumina, tf necessary, a fourth columm with active carbon was used to eliminate background interferences. Samples were analyzed for each of the five chlorinated dibenzo-p-dioxin and dibenzofuran congener groups (with four to eight chlorines) by HRGC/HRMS with a Fisons 8060 Gas Chromatograph equipped with a 60 m DB-5 (J & W Scientific) fused silica capillary column (0.25 mm ID, 0.25 ~tm film) coupled to a VG-AutoSpec Ultima Mass Spectrometer operating in the El mode at 10.000 resolving power. Quantitative determinations of PCDD/F were performed by an isotope dilution method using relative response factors previously obtained from five calibration standard solutions (Chemsyn Science Laboratories) [16,20]. A blank sample was analyzed for every batch of 6 samples. Recoveries of internal standards, as determined against external standard, generally varied between 80-110%. The relative standard deviation of the method was 15%. Total organic carbon was determined using an elemental analyzer (Carlo Erba EA1108). The organic carbon content was quantified after removing inorganic carbon (carbonates) with HCI 2N and neutralized with CaO. All samples were analyzed in duplicates. Determination of dry matter content was achieved by drying subsamples (1-3 g) at 130°C overnight [16].

Data analysis In the case of values under the detection limit, I-TEQ calculations were carried out assuming that the congener

422 was present at one-half o f that value. A multivariate analysis o f the results was done. Data matrices were evaluated by means o f Principal C o m p o n e n t Analysis (PCA). This approach is useful to determine whether more than one potential emission source could explain the presence o f P C D D / F s in the soil samples. Each sample was assigned a score in each component thus allowing the summarized data to be further analyzed and plotted. All calculations were performed using the statistical software SPSS-6.1.

RESULTS AND DISCUSSION

Table 1 shows the concentrations o f PCDD/Fs in the 24 soil samples recently collected near a MSWI. PCDD/F levels obtained in the 1996 study [16], as well as the percentage o f temporal variation for each sample taken in the same sampling point in 1996 and again in 1997 are also given. Most tetra to octa-PCDD/Fs could be detected in all samples. In the previous survey, 2,3,7,8-TCDD was identified in 18 o f the 24 samples, with the highest concentration being 0.07 ng/kg (dry matter). In the present survey, 2,3,7,8-TCDD was detected in 20 o f the 24 samples, with the highest level being 0.13 ng/kg (dry matter).

Table 1. Concentrations of PCDD/F in soil samples collected in the vicinity of a municipal solid waste incinerator" Samples and Distances from MSWI

I-TEQ PCDDs 1996

1997

NE1 250m 0.35 0.54 NW1 250m 0.76 0.51 SEI 250 m 0.40 0.52 SW1 250m 0.27 0.51 NE2 500m 0.10 0.29 NW2 500 m 0.38 0.20 SE2 500m 0.31 0.36 SW2 500m 0.09 0.18 NE3 750 m 0.36 0.17 NW3 750m 0.16 0.21 SE3 750 m 0.37 0.25 SW3 750m 0.16 0.20 NE4 1000m 0.13 1.92 NW4 1000m 0.19 0.57 SE4 1000m 0.15 0.44 SW4 1000m 0.33 0.29 NE5 1250m 0.27 0.42 NW5 1250m 0.19 0.02 SE5 1250 m 0.25 0.32 SW5 1250m 0.13 0.18 NE6 1500m 1.50 0.22 NW6 1500m 0.17 0.87 SE6 1500m 0.27 0.39 SW6 1500m 0.33 1.21 'Results are given in ng/kg (dry matter)

I-TEQ PCDFs %

1996

1997

+54 -33 +30 +89 +190 -47 +16 +100 -53 +31 -32 +25 +1377 +200 +193 -12 +56 -89 +28 +38 +85 +412 +44 +227

0.14 1.83 1.01 0.67 0.13 1.42 0.32 0.15 0.90 0.45 0.53 0.26 0.40 0.81 0.41 1.37 0.46 0.24 0.61 0.43 4.42 0.44 0.67 0.66

1.15 1.13 0.56 0.90 0.50 0.36 1.05 0.46 0.62 0.37 0.29 0.30 1.96 1.37 0.68 0.59 0.76 0.10 0.57 0.54 0.38 2.47 0.37 0.58

RATIOS % +721 -38 -45 +34 +285 -75 +228 +207 -31 -18 -45 +15 +390 +69 +66 -57 +65 -58 -7 +26 -91 +461 -45 -12

I-TEQ TOTAL

1996

1997

1996

2.47 0.42 0.40 0.41 0.73 0.27 0.98 0.58 0.40 0.36 0.69 0.62 0.34 0.23 0.37 0.24 0.60 0.80 0.40 0.30 0.34 0.38 0.40 0.51

0.47 0.45 0.92 0.57 0.58 0.56 0.34 0.40 0.28 0.58 0.87 0.68 0.98 0.41 0.65 0.48 0.55 0.19 0.55 0.34 0.57 0.35 1.06 2.08

0.47 2.57 1.30 0.91 0.22 1.71 0.62 0.23 1.26 0.61 0.90 0.42 0.53 1.00 0.57 1.70 0.74 0.41 0.86 0.56 5.80 0.60 0.93 0.99

1997 1.69 1.65 1.08 1.41 0.79 0.57 1.42 0.64 0.79 0.56 0.54 0.50 3.88 1.94 1.11 0.88 1.18 0.11 0.88 0.72 0.60 3.34 0.76 1.80

% +260 -36 -17 +55 +259 -67 +129 +178 -37 -8 -40 +20 +632 +94 +95 -48 +59 -73 +2 +29 -90 +457 -18 +82

The current PCDD/F levels ranged from 0.11 to 3.88 ng I-TEQ/kg (dry matter) with a median value o f 0.88 ng I-TEQ/kg (dry matter) and a mean value o f 1.17 ng I-TEQ/kg (dry matter). The highest mean (I-TEQ) concentration was found at 1000 m from the stack to N E direction, whereas the lowest level was seen at 1250

423 m from the plant to N W direction. In the 1996 survey, PCDD/F concentrations ranged from 0.22 to 5.80 ng ITEQ/kg (dry matter) with median and mean values o f 0.80 and 1.08 ng I-TEQ/kg (dry matter), respectively. A comparison with the current mean values shows an increase o f 8.3% in the PCDD/F levels during the last year. It has been shown that the PCDD/PCDF ratio can be a useful parameter to identify the PCDD/F sources [7]. In the present survey, PCDD/PCDF ratios between 0.19 and 2.08 (mean value 0.62) were found, whereas in the 1996 study PCDD/PCDF ratios ranged between 0.23 and 2.47 (mean value 0.55). According to this, it seems that during the last year the emission source(s) o f PCDD/Fs in the area under study were basically the same. The levels o f PCDD/Fs according to the four main wind directions in the area are shown in Table 2 for the 1996 and 1997 surveys. As in the 1996 survey, in the current study the highest PCDD/Fs levels were found to NE (mean values: 1.50 [1996 study] and 1.44 [current study] ng I-TEQ/kg, dry matter) and NW directions (mean values: 1.15 [1996 study] and 1.37 [current study] ng I-TEQ/kg, dry matter). With the exception o f the samples to NE direction, in which a slight decrease (4%) could be observed, PCDD/F levels in soils increased during the last year. The calculated total I-TEQs in soil samples in the 1996 and 1997 monitoring programs for the four main wind directions are also shown in Figure 1. The differences in the levels of PCDD/Fs between both surveys did not reach the level o f statistical significance (p < 0.05).

Table 2: Concentrationsof PCDD/F in soil samplescollectedaccordingto the four main wind directionsin the vicinityof a municipal

solid waste incinerator' NE 1996 2,3,7,8-TCDD 1,2,3,7,8 PeCDD 1,2,3,4,7,8-HxCDD 1,2,3,6,7,8-HxCDD 1,2,3,7,8,9-HxCDD 1,2,3,4,6,7,8-HpCDD OCDD 2,3,7,8-TCDF 1,2,3,7,8 PeCDF 2,3,4,7,8 PeCDF 1,2,3,4,7,8-HxCDF 1,2,3,6,7,8-HxCDF 1,2,3,7,8,9-HxCDF 2,3,4,6,7,8-HxCDF 1,2,3,4,6,7,8-HpCDD 1,2,3,4,7,8,9-HpCDF OCDF

1997

0.05 0.03 0.10 0.27 0.20 0.34 0.54 1.05 0.70 0.96 10.91 12.70 119.6 66.95 1.72 1.15 0.88 0.46 0.70 0.66 1.87 1.84 0.93 0.68 0.18 0.13 0.85 0.83 8.82 5.96 0.79 0.50 28.00 10.92

I-TEQ PCDDs 0.43 0.59 I-TEQ PCDFs 1.07 0.89 PCDD/PCDF 0.40 0.66 I-TEQ (PCDD/Fs) 1.50 1.44 'Results are given in ng/kg (dry matter)

NW 1997

SE

%

1996

-40 +170 +70 +94 +37 +16 -79 -33 -48 -6 -2 -27 -28 -2 -32 -37 -61

0.08 0.04 0.30 0.23 0.24 0.19 0.50 0.54 0.53 0.62 6.15 7.25 3 7 . 0 9 38.00 1.63 0.85 0.50 0.32 0.63 1.07 1.64 1.39 0.64 0.57 0.09 0.17 0.75 0.75 4.05 3.51 0.34 0.32 6.09 6.66

-50 -23 -21 +8 +17 +18 +2 -48 -36 +70 15.2 -11 +89 0 -13 -6 +9

0.04 0.12 0.16 0.41 0.39 5.82 37.79 1.47 0.35 0.42 0.90 0.32 0.10 0.48 2.91 0.20 4.48

0.06 0.17 0.16 0.53 0.51 7.18 37.20 1.21 0.30 0.38 1.07 0.43 0.06 0.67 2.47 0.36 4.82

+50 +42 0 +29 +31 +23 -2 -18 -14 -10 +19 +34 -40 +40 -15 +80 +8

0.03 0.13 0.13 0.25 0.35 3.52 16.64 1.29 0.30 0.39 1.13 0.38 0.17 0.49 2.40 0.29 4.70

0.04 0.11 0.16 0.49 0.54 13.64 74.15 0.57 0.31 0.41 1.04 0.49 0.17 0.64 3.39 0.35 9.11

+33 -t5 +23 +96 +54 -287 -346 -56 +3 +5 -8 +29 -0 -31 ~41 -21 ÷94

+37 -17 -65 -4

0.29 0.86 0.34 1.15

+38 +13 +21 +19

0.28 0.59 0.47 0.86

0.38 0.59 0.64 0.97

+36 0 +36 +13

0.21 0.59 0.36 0.80

0.43 0.56 0.77 0.99

+105 -5 +114 +24

0.40 0.97 0.41 1.37

%

1996

1997

SW %

1996

1997

%

424 The concentrations of PCDD/Fs in soil samples according to the different distances from the stack are given in Table 3. In the 1997 survey, the highest mean (I-TEQ) concentration in soil was found at 1000 m from the MSWI (1.95 ng I-TEQ/kg, dry matter). High PCDD/F levels were also observed at 1500 m from the stack (1.62 ng I-TEQ/kg, dry matter) and near the incinerator, 250 m (1.46 ng I-TEQ/kg, dry matter). In the 1996 survey, the highest PCDD/F levels were found at 250 m from the stack (1.11 ng I-TEQ/kg, dry matter), followed by those found in samples collected at 1500 m (0.96 ng I-TEQ/kg, dry matter). Notwithstanding, there were no significant differences in PCDD/F concentrations in samples taken at different distances from the MSWI. The finding of high PCDD/F levels near the stack can be attributed to fugitive emissions during storage, handling, and transport of ashes. Also, wet deposition may play an important role in increasing the concentrations of PCDD/Fs near the stack. The PCDD/F levels (I-TEQ) in soil samples collected at different distances from the stack in 1996 and again in 1997 are also depicted in Figure 2.

j/ // i

1996

1997

,/

1.6

1.4 1.2

O)

1 ¢.v

0.8

O

0.6

LU

0.4 0.2 0 NE

NW

SE

SW

Wind directions Fig.l. PCDD/F levels in soils collected in the vicinity of a new MSWl (Tarragona, Spain) according to the main wind directions in the area i1996 2.5

;1997i

•

2 O)

1.5

o uJ

1

0.5

250

500

750

1000

1250

1500

Distancesfrom stack (m) Fig.2. PCDDF/levels in soils collected at increasing distances from a new MSWI (Tarragona, Spain).

0.52 0.94 0.55 1.46

0.33 0.83 0.40 1.11

I-TEQ PCDDs I-TEQ PCDFs PCDD/PCDF I-TEQ (PCDD/Fs)

"Results are given in ng/kg (dry matter)

0.06 0.22 0.34 0.83 0.89 9.12 51.43 1.14 0.50 0.55 2.14 0.90 0.08 1.24 6.73 0.67 10.24

0.03 0.24 0.13 0.32 0.31 5.02 70.10 1.64 0.41 0.64 1.63 0.47 0.13 0.71 3.15 0.33 2.91

1997

2,3,7,8-TCDD 1,2,3,7,8 PeCDD 1,2,3,4,7,8-HxCDD 1,2,3,6,7,8-HxCDD 1,2,3,7,8,9-HxCDD 1,2,3,4,6,7,8-HpCDD OCDD 2,3,7,8-TCDF 1,2,3,7,8 PeCDF 2,3,4,7,8 PeCDF 1,2,3,4,7,8-HxCDF 1,2,3,6,7,8-HxCDF 1,2,3,7,8,9-HxCDF 2,3,4,6,7,8-HxCDF 1,2,3,4,6,7,8-HpCDD 1,2,3,4,7,8,9-HpCDF OCDF

1996

250 m

+56 +13 +37 +32

+100 -8 -161 +159 +187 +82 -27 -30 +22 -14 +31 +91 -38 +75 +114 +103 +252

%

0.19 0.23 0.83 0.43

0.03 0.07 0.15 0.29 0.17 4.57 21.54 0.86 0.28 0.13 0.26 0.10 0.07 0.16 0.76 0.09 1.08

1996

0.26 0.59 0.44 0.85

0.02 0.17 0.19 0.40 0.37 329 18.42 1.10 0.26 0.47 0.79 0.43 0.30 0.49 2.29 0.34 4.59

1997

500 m

+37 +157 -47 +98

-33 +143 +27 +38 +118 -28 -14 +28 -7 +261 +204 +330 +329 +206 +201 +278 +325

%

0.26 0.49 0.53 0.75

0.02 0.08 0.14 0.31 0.31 6.67 52.27 1.18 0.21 0.31 0.78 0.25 0.09 0.47 3.69 0.25 3.11

1996

0.21 0.39 0.54 0.60

0.02 0.12 0.12 0.34 0.33 2.79 18.50 0.52 0.15 0.34 0.64 0.34 0.04 0.42 1.67 0.19 2.86

1997

750 m

-19 -20 +2 -20

0 +50 -14 +10 +7 -58 -65 -56 -29 +10 +18 +36 -56 -11 -55 -24 -8

%

0.26 0.61 0.43 0.78

0.02 0.09 0.11 0.23 0.29 3.35 16.56 1.55 0.37 0.52 0.83 0.29 0.10 0.36 1.59 0.14 1.46

1996

0.80 1.15 0.70 1.95

0.08 0.40 0.43 1.35 1.33 14.75 65.18 1.56 0.54 0.88 2.45 0.81 0.09 1.12 6.53 0.58 8.98

1997

1000 m

+208 +89 +63 +150

+300 +344 +291 +487 +359 +340 +294 +1 +46 +69 +195 +179 -10 +211 +311 +314 +515

%

0.21 0.45 0.47 0.65

0.02 0.13 0.12 0.33 0.34 4.37 27.16 0.99 0.26 0.33 0.61 0.26 0.11 0.37 2.00 0.20 2.80

1996

0.23 0.49 0.47 0.72

0.03 0.10 0.10 0.35 0.41 4.61 29.18 0.82 0.24 0.32 0.92 0.38 0.08 0.51 2.62 0.28 14.74

1997

1250 m

+10 +9 0 +11

+50 -23 -20 +6 +20 +5 +7 -17 -8 -3 +51 +46 -27 +38 +31 +40 +426

%

Table 3: concentrations of PCDD/F in soil samples collected at increasing distances from a municipal solid waste incinerator ~

0.30 0.66 0.45 0.96

0.05 0.11 0.20 0.42 0.66 3.71 15.52 1.54 0.38 0.45 1.00 0.49 0.06 0.58 3.28 0.36 15.07

1996

0.67 0.95 0.70 1.62

0.04 0.18 0.12 0.65 0.61 26.60 141.7 0.54 0.38 1.24 1.06 0.38 0.20 0.55 3.15 0.25 5.84

1997

1500 m

+123 +44 +56 +69

-20 +64 -40 +55 -8 +617 +813 -65 0 +176 +6 -22 +233 -5 -4 -31 -61

%

L~

426 On the other hand, to correlate the PCDD/F data in soil samples during the two monitoring periods, 1996 and 1997, and to evaluate potential changes in the isomer distribution (i.e., as a result of chemical reactions, volatilization, or dechlorination), PCA was applied to the 24 soil samples collected during the 1997 survey, together with those (24 samples) taken at the same points during the 1996 sampling. This analysis provided a single two-dimensional model, which would explain 78.4% of the variance in the data. The first main PC (which would explain 47.6% of the variance) was strongly and positively correlated with the furans, while the second PC (30.8% of the variance) was correlated with TCDD, PeCDD and all the HxCDDs. The scatterplot of the component scores on both PC is depicted in Figure 3. One main cluster can be identified. Only two samples NE6 and NE4 corresponding to the 1996 and 1997 surveys are outside the cluster and can be considered as outliers. PCDD/F levels in these samples would be basically due to emission sources other than the MSWI. The estimated quantities of PCDD/Fs emitted by a MSWI can be calculated by multiplying an emission factor (the amount of PCDD/Fs emitted per kg of material combusted) by the solid waste burned [11]. To determine if additional emission sources other than the MSWI are also responsible for the PCDD/F levels (I-TEQ) found in soils, the quantities of PCDD/Fs deposited in soils during the last year were estimated. In the case of this MSWI, PCDD/F emission was about 1 ng I-TEQ/m3, while the flow was 38,000 (N)m3/h. It would mean an annual emission of PCDD/Fs from the plant of 0.33 g I-TEQ/year. The emission rates for PCDD/F from MSWIs have been reported to be between 0.018 and 27 ng I-TEQ/m 3 [9]. Taking into account a vertical mobility of PCDD/Fs in surface soils between 0 and 10 cm, a soil density of 1.4 g/cm 3, as well as a surface with a radius of 3 km around the MSWI, the PCDD/F concentrations in soil should be increased in 0.08 ng I-TEQ/kg of soil (dry matter). No degradations or volatilizations of PCDD/Fs have been supposed. Since this estimation (0.08 ng I-TEQ/kg of soil) agrees well with the current results (an average increase of 0.09 ng I-TEQ/kg of soil during the last year), it can be concluded that no remarkable sources of PCDD/F emissions other than the MSWI are present in the examined area.

©

6 5 4 t~ nO IO <

3 2

,,3. . . . . . . . . . . . . . . . . . . . .

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FACTOR

. 3 1

Pr,nc,pa, c o m p o n e n , - - , s : p,ot

for samples collected in the vicinity of a new MSWI (Tarragona, Spain) in 1996 and again in 1997

1

¢~ 1997 W 1996

4

427 Automobile exhaust, especially from leaded gasolines, is also an important potential source of PCDD/F emissions [5,9,21]. However, since 1985 unleaded gasolines are being used in Spain, while a reduction to 0.15 g Pb/1 has been also carried out in leaded gasolines. Consequently, according to the above estimation it seems that PCDD/F emissions from automobiles would not be a significant source of these compounds in the area under influence of the MSWI. Bruzy and Hites [ 11 ] showed that soil acts as a conservative matrix for the collection of atmospheric deposition of PCDD/Fs. In turn, Trapp and Matthies [22] investigating volatilizationof PCDD/Fs from soil with a mathematical model concluded that for background conditions, air and soil are close to equilibrium and desorption from soil plays a minor role even when soil concentrations are above chemical equilibrium to air. However, when soils are highly polluted volatilization can be important. The results of the current survey show that, in terms of mean and median values, PCDD/F concentrations in soils collected in the vicinity of the MSWI were not altered during the last year. While the increases in PCDD/F concentrations could be interpreted as a direct influence of the MSWI, since the operation conditions of the plant were basically unchanged during the last year, the decreases (and probably also the increases) found in the present survey could be explained taking into account the heterogeneity of the samples rather than the influence of processes such as volatilization, degradation or other mechanisms that are controlled by the characteristics of the congeners and the environment. The PCDD/F concentrations fotmd in the present study are similar or lower than the levels of PCDD/F recently reported in soil samples collected in the vicinity of MSWIs from the Netherlands [23,24], USA [25], and Spain [26]. The current I-TEQs were < 5 ng/kg (dry matter), a limit which should restrict the cultivation of certain vegetables [27]. If the same rates of PCDD/F emissions from the MSWI here assessed are maintained in the future, PCDD/F concentrations in soil would reach that limit (5 ng I-TEQ/kg, dry matter) in about 12 years. However, since to reduce metal, PCDD/Fs and other emission products, a new equipment has been recently installed in the plant, it is expected that emissions from the stack will be remarkably reduced. The efficacy of the new equipment on the environmental levels of metals and PCDD/Fs will be assessed in the near future.

ACKNOWLEDGEMENTS This study was supported financially by SIRUSA (Tarragona, Spain).

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