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Environmental contamination and seasonal variation of metals in soils, plants and waters in the paddy fields around a PbZn mine in Korea
the Science of the Total Emhnment AL! I-Ja.nulrr-Pnwh I”,~ u* F.a,i-ti.nd!aII-,Np “alM”l The Science of the Total Environment 198 (1997) 105-121
Environmental contamination and seasonal variation of metals in soils, plants and waters in the paddy fields around a Pb-Zn mine in Korea Myung Chae Jung*, Iain Thornton Environmental
Geochemistry
Research,
Centre for Environmental Technology, London, SW7 2BP, UK
Royal School
of Mines,
Imperial
College,
Received 4 October 1996; accepted 7 January 1997
Abstract The objective of this study is to investigatethe extent and degreeof heavy metal contamination of paddy fields influenced by metalliferous mining activity. Paddy soils,rice plants and irrigation waters were sampledalong six traverse lines in the vicinity of the mine and nearby control site. Soil sampleswere taken 30, 80 and 1.50days after rice transplanting,to study seasonalvariation of their chemicalpropertiesand heavy metal concentrations.Sampling of rice plants and irrigation waters was alsoundertakenwith seasons.The analysisof the sampleswere carried out using ICP-AES for 25 elementsincluding Cd, Cu, Pb and Zn. Physical and chemical properties of soils (pH, loss-on-ignition,cation exchangecapacity and texture) and waters (pH, Eh and temperature) were also measured. The properties of soilswere similar to the averageKorean soils,with the exception of somesamplestaken in the vicinity of the mine. Concentrationsof Cd, Cu, Pb and Zn in paddy soils,rice plantsand irrigation waterssampledin the immediatevicinity of the mine were relatively high due to the seepageof metals from mining dump sites. Although there wasvariation between samplingsites, soil pH values under reducing conditionswere on average higher than those under oxidising conditions. Relatively low content of organic matter and low cation exchange capacity of soils were found at 80 days after rice transplanting (P < 0.05). No seasonalvariations in metal concentrationswere found in paddy soils throughout the period of the rice growing, in which soilsranged from flooded reducing conditions through most of the growing seasonto drained oxidising conditions before and at harvest.Relatively high metal concentrationswere found in the rice stalksand leavesunder oxidisingconditions.The sequentialextraction analysisof selectedsoil samplesconfnmed that high proportions of exchangeablefractions of the metalswere found under oxidisingconditions. It was shownthat Cd and Zn concentrationsin rice leaves and stalksand rice grain increasedwith increasingmetal concentrationsin paddy soilsto a greater extent than for Cu and Pb. This difference in uptake is in agreementwith the greater proportionsof Cd and Zn, comparedwith Cu and Pb,
*Corresponding author. Department of Mineral and Petroleum Engineering, College of Engineering, Seoul National University, Seoul, 151-742, Korea. 0048-9697/97/$17.00 PII
SOO48-9697(97)
0 1997 Elsevier Science B.V. All rights reserved. 05434-X
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in the exchangeable soil fraction extracted with MgCI,. Average daily intake from locally grown rice by the residents wasestimatedto be 121 pg Cd and 126 pg Pb. Thus, long-term metal exposureby regular consumptionof the rice posespotential health problemsto residentsin the vicinity of the mine, although no adversehealth effects have as yet been observed. 0 1997Elsevier ScienceB.V. Environmental contamination; Heavy metals; Seasonalvariation; Rice (Oyzu satiuaL.); Metalliferous mine; Korea
Keywords:
1. Introduction In Korea, rice is the most common crop grown on agricultural land. The total area of paddy soils (irrigated land) has been estimated as 1270000 hectares and up to 32.6% of these are well cultured with high production of rice and the others are poorly cultivated with low production [l]. The production of rice in 1990 was 6 630 000 metric tonnes [2]. It is thought that the dietary cereal intake (mainly rice) by a Korean national is 574 g day-‘, which is about half of the total dietary intake [3]. Thus, heavy metals present in rice may have a large influence on metal intake by the Korean population. Many studies have been undertaken into metal concentrations in rice from various countries [4-71. Masironi et al. (1977) reported average concentrations of metals in polished rice samples from 22 countries of 0.029 pg Cd gg’, 3 pg Cu g--l, 0.012 pg Cr gg’ and 13.7 pug Zn gg ’ (dry weight, dry wt.) [4]. Watanabe et al. (1989) reported geometric mean contents of Cd and Pb in rice of 0.020 pg g-’ and 0.016 rug gg’ (dry wt.>, respectively [5]. In Korea, it has been suggested that Cd concentrations in rice grain grown on soils developed from cadmium-rich uraniferous black shales ranged from 0.1 to 3.5 pg g-’ (dry wt.), with an average content of 0.6 pug g-’ (dry wt.) [fl]. Because rice is generally grown under both oxidising and reducing soil conditions, these conditions may influence metal uptake by rice plants [9-l 11. Many investigators have demonstrated that the availability of metals decreased under submerged conditions due to the precipitation as hydride, carbonate, sulphide and iron compounds [3J2].
The objectives of this present study are: (1) to
investigate the extent and degree of heavy metal contamination of paddy soils, rice plants and irrigation waters influenced by metalliferous mining activity; (2) to examine seasonal variations of metals in paddy fields throughout rice growing; (3) to determine factors affecting metal uptake by rice; and (4) to study the chemical forms of metals in paddy soils. 2. Materials and methods
The study area around the Sambo Pb-Zn mine is located in northwest Korea, 60 km from the capital city, Seoul. The bedrock in which the mineralisation occurs is biotite schist and muscovite schist with intercalation of quartzite, quartz schist and limestone. The ore minerals are galena (PbS) and sphalerite (ZnS). A detailed description of the area has been published elsewhere [13]. Soils, irrigation waters and rice stalks and grain were sampled along six traverse lines around the mining area. Soils and rice stalks were sampled at 30, 80 and 150 days after transplanting the rice. Irrigation water was collected at 30 and 80 days after transplanting; no water samples were available at 150 days. Rice grain was sampled at harvest (150 days after transplanting). Surface soil samples (O-15 cm depth) were collected with a 2.5 cm diameter hand auger. Each soil sample comprised a composite of nine subsamples taken across a 1 x 1 m2. Subsurface soils were sampled at 15-cm intervals to a maximum depth of 45 cm, each being a composite of at least three subsamples. Samples were placed in clean paper bags and labelled. After air-drying at 25°C for 72 h, samples were disaggregated, sieved to < 2 mm and then ground to a fine powder in a TEMA mill. The < 2 mm fraction was used for
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measuring soil pH, organic matter content (using the loss-on-ignition method), cation exchange capacity and soil texture analysis. The finely milled soil (< 180 km) was used for chemical analysis. Soils were digested in a 4:l ratio of concentrated nitric acid and perchloric acid and leached with hydrochloric acid. The solutions were analysed by Inductively Coupled Plasma Atomic Emission Spectrometry (ICP-AES) [14]. Random samples of rice (Ovzu s&vu L.) stalks and grain were taken along six traverse lines with stainless steel scissors. Hull was removed from grain. Samples of stalks and grain were thoroughly washed in deionised water (DIW), dried in a clean room at ambient temperature for 5 days and milled to a fine powder. Samples were decomposed with concentrated fuming nitric acid and perchloric acid and leached with hydrochloric acid. The solution were analysed by ICP-AES [141. Irrigation waters were filtered using a handpump water on site through a 0.45~Frn membrane filter paper (4.5 cm diameter). After immediate acidification (pH < 1) with concentrated hydrochloric acid, the samples were stored in a cool box. Ten millilitres (9 ml water + 1 ml lanthanum solution) were evaporated in a test tube in an aluminum block at 99°C until approximately 1 ml remained. This was analysed by ICP-AES with variations in final volume compensated for by the internal standard of lanthanum added before the evaporation [ 1.51. A rigorous quality control programme was implemented which included reagent blanks, duplicate samples, in-house reference materials and certified international reference materials [ 161. The precision and bias of the chemical analysis was less than 10%. 3. Results and discussion 3.1. Physical and chemical properties of paddy fields
The physical and chemical properties of paddy soils sampled along the six traverse lines are summarised in Table 1. Soil pH values are similar to the average of 5.7 in Korean soils [ll. Some samples from the vicinity of the mine, however,
198 (1997)
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have a relatively low pH (< 5.0) due to the influence of the weathering of sulphide and gangue minerals. Average loss-on-ignition values are around average for Korean soils of 4.0% [ll. Cation exchange capacity ranges from 8 to 17 meq/lOO g. Because rice grows in muddy or fine grained soils, a relatively high silt fraction is found (70-75% sand, 15-20% silt and 5-10% clay). The pH of irrigation waters ranges from 5.5 to 7.4 (Table 1) with high values due to the past application of calcium carbonate to mine waste water. Average redox potentials of the irrigation waters are 226 mV and 240 mV when sampled 30 and 80 days after transplanting the rice, respectively. The high water temperature (18-25°C) is directly influenced by the air temperature in summer. 3.2. Hea y metal concentrations
Mean concentrations and ranges of Cd, Cu, Pb and Zn in paddy soils are shown in Table 2. Cadmium concentrations range from 0.9 to 1.7 pg -’ at each depth. Soils from the vicinity of the kine have elevated Cd ( > 5.0 pg g- ’ >, whilst much lower concentrations (0.2-0.5 pg gg ’ ) are found in the soils from the control area underlain by the same geology as the mine sites but without mining activities. Surface soils generally contain more Cd than subsurface soils. Because little Cu mineralisation occurs in this area, Cu in the soils is only slightly enhanced ( < 100 pg g-i ). In spite of extensive Pb contamination with l-3% of Pb in upland soils in the mining area [13], concentrations in paddy soils are only moderately elevated ( < 100 pg g-l>, due to immobility of this metal; however few samples exceeded 400 pg g-’ in the immediate vicinity of the mine. High Zn concentrations at the mine dump site (l-3% of Zn> greatly influence the dispersion of this metal in soils around the mine, both laterally and vertically, due to the metals’s high mobility [131. Thus a maximum concentration of 3570 pg Zn g- ’ is found on a terrace adjacent to the mine dump which is partly irrigated with mine waste water. This dispersion of Zn contributes to the enhancement of Zn in paddy soils (> 500 pg Zn g-’ ) in
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Table 1 The physical and chemical properties of paddy soil samples along six traverse lines in the Sambo Pb-Zn mine Before planting rice Depth
CEC beq/ lOOg, Sand (%I Silt (%I Clay (%I
N
Range
5.sa 4.ga
4.0-6.9 4.3-5.3
O-15
PH LOI (%)
Mean
IS-30 30-45 o-15 15-30 30-45
-
4.7a 3.5a
-
o-15 15-30
2.2-9.8 2.6-4.2 -
7.9= 8.2a
30-45
-
o-15 15-30
ND ND -
30-45 o-15 15-30 30-45 n-15 15-30 30-45
ND ND ND ND
o-15 15-30
34 5 0
30-45
6.2-9.9 7.0-9.1
ND ND ND ND ND ND 14 14 14
After 30 days Mean Range 5.5" 5.5" 5.6" 5.4a 5.0b 4.6a 13.2b 12.2b 11.9a 71.9a 75.4a 74.6= 21.7a 14.6a 14.6a 6.5a
4.6-6.5 5.0-6.0 5.0-6.4 3.4-7.5 3.6-7.2 2.5-7.6 7.6-16.6 8.7-16.1 8.6-16.9 67.5-77.0 72.8-78.0 70.0-82.0 14.4-29.3 9.0-12.0 10.0-19s 2.5-12.1 9.0-12.0 8.0-13.0 31 31 31
10.Y ll.oa 31 31 31
After 80 days Mean Range 5.5b 5.4b 5.8b 4.7b 4.6' 4.2b 11.3c 11.2c
4.6-6.5 4.8-6.4 4.8-6.7 3.1-6.4 3.1-6.2 2.0-5.9 7.9-15.1 8.2-15.0 8.1-13.7 68.5-84.9 67.8-77.7 68.0-83.0 9.0-28.5 20.0-27.2 10.8-29.3 3.0-12.2 2.2-7.2 2.2-6.2
10.8b 75.3" 73.8a 75.5= 16.2a 21.9b 20.2b 8.5a 4.3b 4.3b
After 150 days Mean Range 5.3* 5.4a 5.4a 5.2c 4.6d 4.3c 11.3d
10.8d 10.8a 75.4a 76.0a 72.6a 15.0a
15.1C 17.V 9.5a 8.9' 10.4a
4.8-6.4 4.6-6.2 4.8-6.3 3.5-7.3 3.0-6.7 2.5-6.2 7.7-14.3 8.1-13.7 8.3-14.3 70.0-82.0 71.0-81.5 68.7-76.0
11.5-17.5 1X3-20.7 15.0-19.0 6.2-13.0 7.2-10.2 8.0-13.0
ND, not determined; -, no sample taken; azbSignificant difference in adjacent column (the time of sampling) of the same row (soil properties) at P < 0.05. Table 2 Mean concentrations and ranges of Cd, Cu, Pb and Zn in paddy soils sampled along six traverse lines in the Sambo Pb-Zn mine (/+I g-‘) Before planting rice Depth Cd
CU
Pb
Mean
O-15 15-30 30-4s O--l5 15-30 30-45
Range
1.7a
0.6-7.3
0.9"
0.8-1.1 < l-103 15-16 17-408
31 16
O-15 15-30
After 30 days
90 25
20-29
30-4s Zn
N
o-15 15-30
465
30-4s O-1 15-30 30-45
--
188 34 5 0
74-3100 114-379
14 14 14
Mean 1.3a 0.9a 0.9a 35a 28a 28a 84a 79" 79a 627" 134a 345a 31 31 31
After 80 days Range
0.3-5.8 0.2-3.2 0.2-2.7 21-78 14-59 15-63 24-318 23-327 21-361 101-35x 76-1820 76-1460 31 31 31
Mean 1.3" 1.7b
l.oa 33a 34* 28a 85a 1198 78a 507a 656a 442a
Range 0.3-4.3 0.3-7.8 < 0.2-3.2 15-84 12-77 13-62 21-319 21-483
11-411 58-1880 56-3350 56-1480
After 150 days Mean Range 1.6a 1.3a 1.2a 32' 29a 27a 114a 94a 85a 681a 504a 450a
0.3-4.8 0.2-3.9 0.2-3.9 12-77 12-68 12-77 19-483 17-406 16-490 51-3350 52-2180 51-1860
net sample taken. ’ ” Significant difference in adjacent column (the time of sampling) of the same row (metal concentration in soil) at P < 0.05.
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Table 3 The physical and chemical properties and metal concentrations in irrigation waters sampled along six traverse lines in the vicinity of the Sambo Pb-Zn mine After 30 days (N = 14) Cd(figl-‘) cu(~gl-‘) PbtFgI-*) Zn(pgl-‘) Temperature (“0 PH Eh (rnv)
AM
GM
7.Y 9.6a 20.4a 4580a 19.Sa 6.6a 226a
3.7 5.3 14.4 218
After 80 days (N = 31) GM AM
Range 1.0-50.0 1.0-53.0 1.0-67.0 1.0-49 100 18.2-21.3 5.5-7.4 160-296
4.3b 8.5b 12.0b 486b 23.4b 6.8a 240’
Range
3.6 4.1 9.6 60.9
1.0-9.0 1.0-35.0 2.0-35.0 20-8510 21.8-24.6 6.2-7.3 42-368
N, numbers of sample; AM, arithmetic mean; GM, geometric mean. “.bSignificant difference in adjacent column (the time of sampling) for arithmetic mean of the same row (metal concentration and some properties) at P < 0.05..
comparison with those from the control site (< 100 pg Zn g-l). Concentrations of Cd, Cu, Pb and Zn in irrigation waters are summarised in Table 3. Because a large amount of water is needed in the early stage of rice growing, it is inevitable that large quantities of mine waste water will be used in the paddy fields around the vicinity of the mine. Thus, some irrigation waters sampled at 30 days after transplanting contain high concentrations of metals. A wide range of Cd concentrations of 1.0-50 pg 1-l is found, with high levels from the vicinity of the mine (> 10 pg 1-l) and low concentrations from the control site. Concentrations of Cu are similar, ranging from 1.0 to 53 pg 1-l. In spite of the high concentrations of Pb in soils from the mining
area (41-29900 pg g-i) [13], relatively low Pb concentrations are found in irrigation waters of < 67 pg 1-i due to its very low solubility. However, Zn concentrations are high, ranging up to 49100 pg Zn 1-i. It can be expected that such high concentrations of Zn may influence both the composition of paddy soils and metal uptake into rice grain and stalk.1 3 Mean concentrations and ranges of metals in rice stalk and grain samples are shown in Table 4. Concentrations of Cd range from 0.1 to 5.0 pug g-i (dry wt.) in rice stalks and leaves, and from 0.1 to 0.5 /J,g g -I (dry wt.) in grain. It has been reported that Cd concentrations in rice stalk grown on soils developed from cadmium-rich black shale in Korea averaged 1.7 pg g-i (dry
Table 4 Mean concentrations and ranges of Cd, Cu, Pb and Zn in rice stalks and grain sampled along six traverse lines in the vicinity of the Sambo Pb-Zn mine ( pg g-l, dry weight) Rice stalks
Rice grain
After 30 days Mean Cd cu Pb Zn N
0.35a 10.4” 4.9” 95” 14
After 80 days Range
Mean
Range
0.20-0.70 5.3-22.6 3.1-10.3 27-486 31
0.46” 9.5a 2.ga 74” 31
0.20-1.50 4.6-20.4 1.6-8.8 24-415 31
After 150 days
After 150 days Mean 0.77b 9.7a 5.8b 137b
Range 0.10-5.00 6.1-20.1 3.0-16.9 20-471
Mean 0.21C 3.0a 0.2za 25.2a
,
Range 0.10-0.50 1.2-5.8 < 0.1-0.6 19.0-37.0
“bSignticant difference in adjacent column (the time of sampling) of the same row (metal concentration in rice stalk) at P < 0.05. N, numbers of sample.
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wt.), ranging from 0.1 to 6.6 pg g-’ (dry wt.) and 0.6 pug g-’ (dry wt.) with a range of 0.1-3.5 pg g-’ (dry wt.> in rice grain 181. Watanabe et al. (1989) reported that the geometric mean Cd in worldwide rice grain (n = 207) was 0.02 pg g-’ (dry wt.); they also reported that Cd levels in Korean rice grain averaging 0.016 pg gg’ (dry wt.), with a range of 0.006-0.045 pg g-’ (dry wt.) [5]. In comparison with their data, rice grain in the present study contains about 20 times greater Cd levels. Copper concentrations in rice stalk and leaf range from 9.5 to 10.4 pg g-’ (dry wt.> and in rice grain from 1.2 to 5.8 ,ug gg’ (dry wt.) (Table 41. According to Masironi et al. (1977) [4], worldwide Cu concentrations in rice grain (n = 100) average 4.0 pg g -’ (dry wt.) (unpolished) and 3.0 pg g-’ (dry wt.) (polished). Lidon and Henriques (19921 reported a Cu toxicity when rice contained 35.1 pug g-’ (dry wt.> 1171. With the exception of some rice stalk (> 15 pg g-‘, dry wt.), most samples have relatively low Pb concentrations, ranging from 2.8 to 5.8 pg g-’ (dry wt.> (Table 4). Watanabe et al. (1989) reported a worldwide geometric mean value of 0.016 pg gg ’ (dry wt.) in rice grain, with a range of 0.004-0.032 pg g-’ (dry wt.) [5]. They also found that Pb in Korean rice grain averaged 0.012 pg gg ’ (dry wt.), with a range of 0.004-0.032 pg g-’ (dry wt.). In comparison with their data, rice grain samples reported here ( < 0.1-0.6 pg g-‘, dry wt.) contain about 20 times higher Pb levels. Zinc concentrations in rice samples range from 74 to 137 pg g-’ (dry wt.) in the stalk samples and from 19 to 37 pg gg’ (dry wt.) in the grain samples, which are higher than worldwide Zn concentrations of 16.4 pg g-’ (dry wt.) (unpolished) and of 13.7 pg g-’ (dry wt.) (polished) reported by Masironi et al. (19771 [4]. High concentrations of Zn in the rice samples are strongly influenced not only by those in the paddy soils and irrigation waters but also the high bioavailability of Zn to plants. S..?. Seasonal variation Many workers have found increasing soil pH under submerged conditions, especially in acid soils [3,10,18]. When paddy soils are flooded, the
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diffusion of 0, into the soils and CO, out of the soil is greatly restricted, resulting in the accumulation of CO, [11,12]. This increases the concentrations of HCO; and CO:- in the soil solution and may cause elevation of soil pH and precipitation of metals. Although variation is found between sampling sites, surface soil pH under reducing conditions (30 and 80 days after transplanting rice) is higher than that under oxidising conditions (150 days after) (Fig. 1). Statistically significant difference in soil pH is found between 80 and 150 days after planting the rice (P < 0.05) (Table 1). Thus the soil pH generally decreases in the order: 80 days 2 30 days > 150 days after planting. Similar results are also found in the subsurface soils (15-45 cm depth). The organic matter content of surface soils, measured by losson-ignition, shows that soils sampled at 80 days have lower organic matter contents than those at 30 and 150 days after (P < 0.05) (Fig. 1). Similar results are also found in subsurface soils (Table 1). The seasonal variation in cation exchange capacity of surface soils is similar to that in organic matter. There is little seasonal variation in water pH and Eh. However, a relatively high water temperature is found at 80 days after rice transplanting (P < 0.05) due to an increase in the air temperature during August (Table 3). There is little variation in metal concentrations in paddy soils throughout the period of rice growing (Fig. 2). In the highly contaminated soils, however, soils taken at 30 and 150 days contain higher metal contents that those at 80 days after. Relatively high metal concentrations are found in irrigation waters sampled at 30 days compared with 80 days (P < 0.05) (Table 3). These elevated levels of metals may be derived directly from the mine waste water and from rain water that has infiltrated and passed through the mine dumps. Seasonal variation of metal concentrations in rice stalk is presented in Fig. 3. The figure shows that rice stalks and leaves sampled at 30 days and 150 days after transplanting contain higher metal concentrations than those sampled at 80 days (P < 0.05). Relatively low metal concentrations in rice growing under reducing conditions may be due to their precipitated as hydroxide, carbonates, sulphide and iron compounds [3,9,12].
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q 0
I
u 11
8
6O
I 1
2
3
4
5
6
7
8
q
9
I
m
I 10
11
12
13
14
Site numb4x-s m 30 days after
0
8Odaysaiter
0
150 days after
Fig. 1. Seasonal variations in soil pH, loss-on-ignition and cation exchange capacity of surface soils (O-15 cm depth).
3.4. Relationships between metal concentrations in soils, rice and water
Relationships between metal concentrations in rice stalks and surface soils are shown in Fig. 4. From the figure, it can be seen that metal concentrations in rice stalks increase with increasing levels in surface soils (P < 0.001). The rate of increase of metals in rice stalks differs from metal to metals, higher rates for Cd and Zn and lower rates for Cu and Pb. This is assumed to be due to
differences in the solubility and bioavailability of these metals. Positive correlations between metal concentrations in rice grain and surface soil are also found (P < 0.001) (Fig. 5). Significant correlations are also found between metal concentrations in rice stalks and grain (Fig. 6). 3.5. Factors affecting metal uptake by rice
Many researchers have investigated factors influencing metal uptake by rice. These factors included soil pH [10,12,19], redox potential [11,18],
M.C. Jung, I. Thornton /The Science of the Total Environment 198 (1997) 105-121
112
of most important factors affecting metal bioavailability is soil pH. A relatively low metal
organic matter content 120,211, phosphorous content 122,231, temperature [24] and time 1251. One
.Ei a
1. 10 -;0
,
I 1
2
3
4
I 5
6
7
8
9
10
I 12
11
, 13
Site numbers cl
/ m30daysaik c
Fig. 2. Seasonal variations in
metal
80daysafter
G
150days
concentrations of surface soils (O-15
after
cm depth).
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M.C. Jung, I. Thornton /The Science of the Total Environment 198 (1997) 105-121
113
0 0
0.6
Ef
O
0
q m
0 0
m 0.3
0.0
’
,
I
I
I
1
ii P I
1
I
1
25 m 20 -
B
1s -
12
1 m
0 90 m 6-
g
3-
0
6 0
lo’ , 0 1
0
X
0
0
0
0
0
0” B
8 m
m30daysatIer
3
4
0
0
m 0
I 2
0
M
m 0 0
m
0
I 5 0
I 1 6 7 8 9 Site numbers 80days&er
0 •El
m q 0
! 10 0
11
12
/ 13
14
150daysafter
I
I
Fig. 3. Seasonal variations in metal concentrations of rice stalks and leaves.
uptake by rice was found under reducing condition due to increasing soil pH [lo]. This study also
shown that metal concentrations in rice stalks growing under reducing conditions are lower than
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Cd in surfacesoil (jg/g)
Y = 2.30 + 0.0177 X (r = 0.75**‘)
F%in sufece soil (rs/g) 500E
Y=22.1 +0.134x(r=o.90*“)
500
1000
1500
2000
2500
3000
3500
2% in Lwrfece soil (18/g) l
**
Significant at p < 0.001
Fig. 4. Relationships between metal concentrations in surface soils (O-15 cm depth) and rice stalks.
those growing under oxidising conditions (see Fig. 3). Many studies found that an increase in soil
organic matter content increases the exchangeable Fe and Mn in soils under flooded conditions
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115
10512I
Cd ia surfacesoil (B/S)
i!O i!o
sb
$0
$0
Cu in surfacesoil (jg/g) Y = 0.0961 + 0.00137X (r = 0.89***)
s q 0.7-
. .
C?
, 50
I 100 I
/ 150
II 200
/
l
**
II 250
II 300
II 350
II 400
II 450
J
Zn in surfacesoil (@g/p) Sigaificantat p
Fig. 5. Relationships between metal concentrations in surface soils (O-15 cm depth) and rice grain.
and decreases the availability of metals to plants [20,21,26]. Because little variation exists in the
organic matter content and cation exchange capacity of soils, no significant relationships are
116
M.C. Jung, I. Thornton / The Science of the Total Environment 198 (1997) 105-121
is cl 0s
Y=O.1SO+O.llOX(r=0.87***)
Cdinricestalk(jg/g,DW)
.
I 10
I a
I 12
I 14
.
.
I 16
I ia
20
Cuinricoaralk(IO/8,Dw) g
OB-
Y=-O.O573
+0.0681X(r=0.78***)
.
/
I .
2.0
3.0
I 4.0
I 5.0
I 6.0
I 7.0
.
T a.0
Pbinriccatdk(Jg/8,Dw) . 5 9
Y=20.7+0.0414X(r=0.89***) 40-
,
50
100
150
200 l
250
300
350
400
450
500
Zn in rice stalk (re/g, DW) ** Si8nifiomt at p < 0.001
Fig. 6. Relationships between metal concentrations in rice stalks and grain.
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found in this study. However, it is concluded ideally that high metal uptake by rice of the paddy soils in this study will be influenced by the low organic matter contents and cation exchange capacity. 3.6. Chemical speciation of paddy soils
Although the total metal concentrations in paddy soils have been shown to influence metal concentrations in rice, the chemical forms of metals in the soils will also affect metal uptake by rice. Many workers have investigated metal speciation and bioavailability in paddy soils using a sequential extraction scheme [27-301. This study has been also applied in this under both reducing and oxidising soil conditions [31]. The results of sequentially extracted metal concentration in selected samples are shown in Fig. 7 and partitioning of the metals in each fraction is presented in Fig. 8. The selected samples were taken sites f‘Rl-SO’ and ‘Rl-150’, ‘R2-80’ and ‘R2-150’ and ‘R3-80’ and ‘R3-150’ at 80 days and 150 days after transplanting, respectively. Under submerged conditions (sample identifications ‘Rl-80’, ‘R2-80 and ‘R3-80’1, Cd and Zn in the soils is largely associated with the Fe and Mn oxide fraction and, to a lesser extent, the carbonate and specifically adsorbed fractions. It has been found that Zn present in amorphous sesquioxide-bound and exchangeable bound forms contributed to Zn uptake by rice [281. Under oxidising conditions (sample identifications ‘R2-150’ and X3-150’), relatively low concentrations of Cd, Pb and Zn are presented in the Fe and Mn oxide fraction, with the exception of sample ‘Rl-80’. In comparison, under reducing conditions, relatively high concentrations of metals are found in the exchangeable fraction, due possibly to the dissolution of metals presented in the Fe and Mn oxides. This result is in agreement with the fact that metal concentrations in rice growing under oxidising conditions are higher than those under reducing conditions. Throughout the period of rice growing, under both flooded and unllooded conditions, there is no significant seasonal variations of metals pre-
I98 (I997)
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sent in the carbonate, organic and residual fractions. 3.7. Implication
to animal and human health
Soils contaminated by various sources may influence the composition of food crops, and the proportion of different crops in the diet may affect the total metal intake by grazing animals. In the study area, cattle and swine are reared on small farms. The common diet of these animals is normally locally grown crops with rice stalks for cattle and corn for swine. As shown in Table 4, metal concentrations in rice stalks and leaves are significantly elevated. These metals can then be directly ingested by cattle. Because rice stalks and leaves are fed to cattle without washing, livestock can also ingest metals in soils adhering to their surface. It was not possible to sample animal tissue from the study area due to lack of resources, however, it is likely that animals in the study area will ingest metals through a diet grown on soils contaminated by the mining activity. Human health may be affected by the amount of chemical elements ingested and inhaled via food, drinking water and atmosphere [32]. The dietary intake of cereal (mainly rice) by Koreans is estimated to be 574 gram per day [3]. The average Cd concentration in rice grain grown in the study area is 0.21 pg g-i (dry wt.). In general, the residents in the study area consume crop plants grown in their own rice fields. When the residents regularly consume rice, the average daily intake of Cd from the rice is up to 120.5 pg (= 574 g day-’ x 0.21 pg g- ‘). This figure markedly exceeds the provisional tolerable weekly intake (PTWI) of 400-500 pg Cd recommended by the FAO and WHO [33]. The average daily intake of Pb intake from the rice by the residents is estimated to be 126 pg (= 574 g day-’ X 0.22 lug g-i), with a range of < 57.4-344 pg; this is about 30% of provisional daily intake of 430 pg recommended by the FAO and WHO [33]. Although human health studies have not been undertaken, regular consumption of the rice by the residents in the study area poses a potential health problem from long-term metal exposure, espe-
Rl-150
IL?-80
R2-150
R3-80 I&150
200
1
5o 0
* 150 r=: 2 100 .5
3
0.5 0
RI-80
R2-80
R2-150
R3-80
Bound onto carbonate Residual fhction
R3-150
0
R1-80
Rl-80
R2-80
Ft2-80
R2-150
RI-150
R3-80
R3-80
Bound onto Fe & Mn oxides
Rl-150
Rl-150
Fig. 7. Diagrams of sequentially extracted metal concentrations in selected paddy soils.
Exchangeable fraction Bound onto organic matter
RI-150
u
.5 10 k op
2 4
Rl-80
4 $j 20
0
30
i
‘;; 2.5
.7J 2 .z 1.5
l
40
-
#- 3.53
R3-150
R3-150
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cially for Cd and Pb and to a lesser extent for Cu and Zn. 4. Conclusions
The physical and chemical properties of paddy soils sampled along six traverse lines around the mine were similar to those reported for Korean soils, with the exception of some soils sampled in the immediate vicinity of the mine which were characterised by low pH, organic matter content, cation exchange capacity and high proportions of sand. Concentrations of Cd, Cu, Pb and Zn in paddy soils and irrigation waters sampled in the vicinity of the mine were higher than those sampled in the control area due to the influence of effluent of metals from mine dump materials. Elevated levels of the metals were also found in rice stalks, leaves and grain taken around the mining area. Although there were variations between sampling sites, soil pH values under reducing soil conditions were higher than those under oxidising conditions (P < 0.051. Statistical differences between 80 days after and 30 days and 150 days after rice transplanting were found in loss-onignition and cation exchange capacity 0’ < 0.05). However, there is little seasonal variation in irrigation water pH and Eh values, and metal concentrations in paddy soils throughout the period of rice growing. This study found that metal concentrations in rice stalks and leaves sampled at 30 days and 150 days after transplanting were relatively higher than those sampled at 80 days (P < 0.051. This result was supported by results from the sequential extraction analysis of selected samples; in comparison with reducing conditions, higher proportions of exchangeable meta fractions was found under oxidising conditions (harvest season). Metal concentrations in rice stalks and leaves increased with increasing metal contents in surface soils (P < 0.001) and the rate of increase of metals in the rice varied from metal to metal, with higher rates for Cd and Zn and lower rates for Cu and Pb due to differences in solubility and bioavailability. Positive correlation of metal concentrations in rice grain and in surface soils (P <
O.OOl), and in rice stalks and leaves and grain (P < 0.001) were also found. Unwashed rice stalks and leaves are an important source of heavy metal intakeby some livestock, especially swine and cattle reared on the small farms around the mine. In addition, The residents living near the mine regularly consume the rice grown on soils contaminated by the mine. The average metal intake from the rice by these residents was estimated to be 120.5 pg day-’ of Cd, which markedly exceeds the guideline of Cd intake recommended by the FAO and the WHO and 126 lug day-i of Pb, which are about 30% of provisional tolerable daily intake of 430 pg recommended by FAO and the WHO 1331. Thus, long-term metal exposure by regular consumption of locally grown vegetables and rice poses potential health problems to residents in the vicinity of the mine, although no adverse health effects have as yet been observed. References Ul MS. Kim, Soils of Korea and their improvement.
Agri-
cultural Science Institute Rural Development Administration, Suwon, Korea, 1985. PI Europa World Year Book, The Europa World Year Book, Europa Publications, 1992. [31 K. Kitagishi and I. Yamane, Heavy metal pollution in soils of Japan. Japan Scientific Societies Press, Tokyo, 1981. [41 R. Masironi, S.R. Koirtyohann and J.O. Pierce, Zinc, copper, cadmium and chromium in the polished and unpolished rice. Sci. Tot. Environ., 7 (1977) 23-43. [51 T. Watanabe, H. Nakatsuka and M. Ikeda, Cadmium and lead in rice available in various areas of Asia. Sci. Tot. Environ., 80 (1989) 175-184. 161 J.C. Fernandes and F.S. Henriques, Heavy metal contents of paddy fields of Alcacer Do Sal, Portugal. Sci. Tot. Environ., 90 (1990) 89-97. PI Z.-S. Chen, Cadmium and lead contamination of soils near plastic stabilizing materials plants in northern Taiwan. Water, Air, Soil Pollut., 57-58 (1991) 745-754. is1 K.W. Kim, and I. Thornton, Influence of uraniferous black shales on cadmium, molybdenum and selenium in soils and crop plants in the Deog-Pyong area of Korea. Environ. Geochem. Health, 15 (1933) 119-133. [91 F.T. Bingham, A.L. Page, R.J. MahIer and T.J. Game, Cadmium availability to rice in sludge-amended soil under ‘flood’ and ‘nonflood’ culture. Soil Sci. Sot. Am. J., 40 (1976) 715-719.
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DOI C.N. Jr. Reddy and W.H. Jr. Patrick, Effect of redox t111 ml (131
[141
1151
iI61
1171
Ml
[191
[201
m
potential and pH on the uptake of cadmium and lead by rice plants. J. Environ. Qual., 6 (1977) 259-262. KS. Sajwan and W.L. Lindsay, Effects of redox on zinc deficiency in paddy rice. Soil Sci. Sot. Am. J., 50 (1986) 1264-1269. D. Dutta, B. Mandal and L.N. Mandal, Decrease in availability of zinc and copper in acidic to near neutral soil on submergence. Soil Sci., 147 (1989) 187-195. M.C. Jung and I. Thornton, Heavy metal contamination of soils and plants in the vicinity of a lead-zinc mine, Korea. Appl. Geochem., 11 (1996) 53-59. M. Thompson and J.N. Walsh, A handbook of Inductively Coupled Plasma Atomic Emission Spectrometty, 2nd edn, Blackie, London, 1988. M. Thompson, M.H. Ramsey and B. Pahlavanpour, Water analysis by inductively coupled plasma atomic emission spectrometry after a rapid pre-concentration. Analyst, 107 (1982) 1330-1334. M.H. Ramsey, M. Thompson and E.K. Banerjee, Realistic assessment of analytical data quality from inductively coupled plasma atomic emission spectrometry. Anal. Pm., 24 (1987) 260-265. F.C. Lidon and F.S. Henriques, Copper toxicity in rice: diagnostic criteria and effect on tissue Mn and Fe. Soil Sci., 154 (1982) 130-135. J.W.O. Jeffery, Detining the status of reduction of a paddy soil. J. Soil Sci., 12 (1961) 173-179. F.T. Bingham, A.L. Page and J.E. Strong, Yield and cadmium content of rice gram in relation to addition rates of cadmium, copper, nickel, and zinc with sewage sludge and liming. Soil Sci., 130 (1980) 32-38. M. Haldal and L.N. Mandal, Influence of soil moisture regimes and organic matter application on the extractable Zn and Cu content in rice soils. Plant Soil, 53 (1979) 203-213. A. Swarup, Influence of organic matter and flooding on the chemical and electrochemical properties of sodic soil and rice growth. Plant Soil, 106 (1988) 135-141.
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L.N. Mandal and M. Haldar, Influence of phosphorus and zinc application on the availability of zinc, copper, iron, manganese and phosphorus in waterlogged rice soils. Soil Sci., 130 (1980) 251-257. Bl M. Haldar and L.N. Mandal, Effect of phosphorus and zinc on the growth and phosphorus, zinc, copper, iron and manganese nutrition of rice. Plant Soil, 59 (1981) 415-425. WI D.Y. Cho and F.N. Ponnamperuma, Influence of soil temperature on the chemical kinetics of flooded soils and growth of rice. Soil Sci., 119 (1971) 184-194. [251 G.T. Gilmour, Micronutrient status of the rice plant: I. plant and soil solution concentrations as a function of time. Plant Soil, 46 (1977) 549-557. WI B. Mandal, G.C. Hazra and A.K. Pal, Transformation of zinc in soils under submerged condition and its relation with zinc nutrition of rice. Plant Soil, 106 (1988) 121-126. WI A.S.P. Murthy, Zinc fractions in wetland rice soils and their availability to rice. Soil Sci., 133 (1982) 150-154. [281 M.V. Singh and I.P. Abrol, Transformation and movement of zinc in an alkali soil and their influence on the yield and uptake of zinc by rice and wheat crops. Plant Soil, 94 (1986) 445-449. 1291G.C. Hazra, B. Mandal and L.N. Mandal, Distribution of zinc fractions and transformation in submerged rice soils. Plant Soil, 104 (1987) 175-181. [301 L.N. Mandal and B. Mandal, Transformation of zinc fractions in rice soils. Soil Sci., 143 (19871 205-212. [311 X. Li, B.J. Coles, M.H. Ramsey and I. Thornton, Sequential extraction of soils for multielement analysis by ICP-AES. Chem. Geol., 124 (1985) 109-123. WI S.H.U. Bowie and I. Thornton, Environmental Geochemistry and Health. D. Reidel Publishing Co., Holland, 1984. [331 WHO, Guidelines for Drinking-water Quality. vol. 1 recommendations. 2nd edn. WHO, Geneva, 1993. t221
Environmental contamination and seasonal variation of metals in soils, plants and waters in the paddy fields around a Pb-Zn mine in Korea Myung Chae Jung*, Iain Thornton Environmental
Geochemistry
Research,
Centre for Environmental Technology, London, SW7 2BP, UK
Royal School
of Mines,
Imperial
College,
Received 4 October 1996; accepted 7 January 1997
Abstract The objective of this study is to investigatethe extent and degreeof heavy metal contamination of paddy fields influenced by metalliferous mining activity. Paddy soils,rice plants and irrigation waters were sampledalong six traverse lines in the vicinity of the mine and nearby control site. Soil sampleswere taken 30, 80 and 1.50days after rice transplanting,to study seasonalvariation of their chemicalpropertiesand heavy metal concentrations.Sampling of rice plants and irrigation waters was alsoundertakenwith seasons.The analysisof the sampleswere carried out using ICP-AES for 25 elementsincluding Cd, Cu, Pb and Zn. Physical and chemical properties of soils (pH, loss-on-ignition,cation exchangecapacity and texture) and waters (pH, Eh and temperature) were also measured. The properties of soilswere similar to the averageKorean soils,with the exception of somesamplestaken in the vicinity of the mine. Concentrationsof Cd, Cu, Pb and Zn in paddy soils,rice plantsand irrigation waterssampledin the immediatevicinity of the mine were relatively high due to the seepageof metals from mining dump sites. Although there wasvariation between samplingsites, soil pH values under reducing conditionswere on average higher than those under oxidising conditions. Relatively low content of organic matter and low cation exchange capacity of soils were found at 80 days after rice transplanting (P < 0.05). No seasonalvariations in metal concentrationswere found in paddy soils throughout the period of the rice growing, in which soilsranged from flooded reducing conditions through most of the growing seasonto drained oxidising conditions before and at harvest.Relatively high metal concentrationswere found in the rice stalksand leavesunder oxidisingconditions.The sequentialextraction analysisof selectedsoil samplesconfnmed that high proportions of exchangeablefractions of the metalswere found under oxidisingconditions. It was shownthat Cd and Zn concentrationsin rice leaves and stalksand rice grain increasedwith increasingmetal concentrationsin paddy soilsto a greater extent than for Cu and Pb. This difference in uptake is in agreementwith the greater proportionsof Cd and Zn, comparedwith Cu and Pb,
*Corresponding author. Department of Mineral and Petroleum Engineering, College of Engineering, Seoul National University, Seoul, 151-742, Korea. 0048-9697/97/$17.00 PII
SOO48-9697(97)
0 1997 Elsevier Science B.V. All rights reserved. 05434-X
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in the exchangeable soil fraction extracted with MgCI,. Average daily intake from locally grown rice by the residents wasestimatedto be 121 pg Cd and 126 pg Pb. Thus, long-term metal exposureby regular consumptionof the rice posespotential health problemsto residentsin the vicinity of the mine, although no adversehealth effects have as yet been observed. 0 1997Elsevier ScienceB.V. Environmental contamination; Heavy metals; Seasonalvariation; Rice (Oyzu satiuaL.); Metalliferous mine; Korea
Keywords:
1. Introduction In Korea, rice is the most common crop grown on agricultural land. The total area of paddy soils (irrigated land) has been estimated as 1270000 hectares and up to 32.6% of these are well cultured with high production of rice and the others are poorly cultivated with low production [l]. The production of rice in 1990 was 6 630 000 metric tonnes [2]. It is thought that the dietary cereal intake (mainly rice) by a Korean national is 574 g day-‘, which is about half of the total dietary intake [3]. Thus, heavy metals present in rice may have a large influence on metal intake by the Korean population. Many studies have been undertaken into metal concentrations in rice from various countries [4-71. Masironi et al. (1977) reported average concentrations of metals in polished rice samples from 22 countries of 0.029 pg Cd gg’, 3 pg Cu g--l, 0.012 pg Cr gg’ and 13.7 pug Zn gg ’ (dry weight, dry wt.) [4]. Watanabe et al. (1989) reported geometric mean contents of Cd and Pb in rice of 0.020 pg g-’ and 0.016 rug gg’ (dry wt.>, respectively [5]. In Korea, it has been suggested that Cd concentrations in rice grain grown on soils developed from cadmium-rich uraniferous black shales ranged from 0.1 to 3.5 pg g-’ (dry wt.), with an average content of 0.6 pug g-’ (dry wt.) [fl]. Because rice is generally grown under both oxidising and reducing soil conditions, these conditions may influence metal uptake by rice plants [9-l 11. Many investigators have demonstrated that the availability of metals decreased under submerged conditions due to the precipitation as hydride, carbonate, sulphide and iron compounds [3J2].
The objectives of this present study are: (1) to
investigate the extent and degree of heavy metal contamination of paddy soils, rice plants and irrigation waters influenced by metalliferous mining activity; (2) to examine seasonal variations of metals in paddy fields throughout rice growing; (3) to determine factors affecting metal uptake by rice; and (4) to study the chemical forms of metals in paddy soils. 2. Materials and methods
The study area around the Sambo Pb-Zn mine is located in northwest Korea, 60 km from the capital city, Seoul. The bedrock in which the mineralisation occurs is biotite schist and muscovite schist with intercalation of quartzite, quartz schist and limestone. The ore minerals are galena (PbS) and sphalerite (ZnS). A detailed description of the area has been published elsewhere [13]. Soils, irrigation waters and rice stalks and grain were sampled along six traverse lines around the mining area. Soils and rice stalks were sampled at 30, 80 and 150 days after transplanting the rice. Irrigation water was collected at 30 and 80 days after transplanting; no water samples were available at 150 days. Rice grain was sampled at harvest (150 days after transplanting). Surface soil samples (O-15 cm depth) were collected with a 2.5 cm diameter hand auger. Each soil sample comprised a composite of nine subsamples taken across a 1 x 1 m2. Subsurface soils were sampled at 15-cm intervals to a maximum depth of 45 cm, each being a composite of at least three subsamples. Samples were placed in clean paper bags and labelled. After air-drying at 25°C for 72 h, samples were disaggregated, sieved to < 2 mm and then ground to a fine powder in a TEMA mill. The < 2 mm fraction was used for
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measuring soil pH, organic matter content (using the loss-on-ignition method), cation exchange capacity and soil texture analysis. The finely milled soil (< 180 km) was used for chemical analysis. Soils were digested in a 4:l ratio of concentrated nitric acid and perchloric acid and leached with hydrochloric acid. The solutions were analysed by Inductively Coupled Plasma Atomic Emission Spectrometry (ICP-AES) [14]. Random samples of rice (Ovzu s&vu L.) stalks and grain were taken along six traverse lines with stainless steel scissors. Hull was removed from grain. Samples of stalks and grain were thoroughly washed in deionised water (DIW), dried in a clean room at ambient temperature for 5 days and milled to a fine powder. Samples were decomposed with concentrated fuming nitric acid and perchloric acid and leached with hydrochloric acid. The solution were analysed by ICP-AES [141. Irrigation waters were filtered using a handpump water on site through a 0.45~Frn membrane filter paper (4.5 cm diameter). After immediate acidification (pH < 1) with concentrated hydrochloric acid, the samples were stored in a cool box. Ten millilitres (9 ml water + 1 ml lanthanum solution) were evaporated in a test tube in an aluminum block at 99°C until approximately 1 ml remained. This was analysed by ICP-AES with variations in final volume compensated for by the internal standard of lanthanum added before the evaporation [ 1.51. A rigorous quality control programme was implemented which included reagent blanks, duplicate samples, in-house reference materials and certified international reference materials [ 161. The precision and bias of the chemical analysis was less than 10%. 3. Results and discussion 3.1. Physical and chemical properties of paddy fields
The physical and chemical properties of paddy soils sampled along the six traverse lines are summarised in Table 1. Soil pH values are similar to the average of 5.7 in Korean soils [ll. Some samples from the vicinity of the mine, however,
198 (1997)
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have a relatively low pH (< 5.0) due to the influence of the weathering of sulphide and gangue minerals. Average loss-on-ignition values are around average for Korean soils of 4.0% [ll. Cation exchange capacity ranges from 8 to 17 meq/lOO g. Because rice grows in muddy or fine grained soils, a relatively high silt fraction is found (70-75% sand, 15-20% silt and 5-10% clay). The pH of irrigation waters ranges from 5.5 to 7.4 (Table 1) with high values due to the past application of calcium carbonate to mine waste water. Average redox potentials of the irrigation waters are 226 mV and 240 mV when sampled 30 and 80 days after transplanting the rice, respectively. The high water temperature (18-25°C) is directly influenced by the air temperature in summer. 3.2. Hea y metal concentrations
Mean concentrations and ranges of Cd, Cu, Pb and Zn in paddy soils are shown in Table 2. Cadmium concentrations range from 0.9 to 1.7 pg -’ at each depth. Soils from the vicinity of the kine have elevated Cd ( > 5.0 pg g- ’ >, whilst much lower concentrations (0.2-0.5 pg gg ’ ) are found in the soils from the control area underlain by the same geology as the mine sites but without mining activities. Surface soils generally contain more Cd than subsurface soils. Because little Cu mineralisation occurs in this area, Cu in the soils is only slightly enhanced ( < 100 pg g-i ). In spite of extensive Pb contamination with l-3% of Pb in upland soils in the mining area [13], concentrations in paddy soils are only moderately elevated ( < 100 pg g-l>, due to immobility of this metal; however few samples exceeded 400 pg g-’ in the immediate vicinity of the mine. High Zn concentrations at the mine dump site (l-3% of Zn> greatly influence the dispersion of this metal in soils around the mine, both laterally and vertically, due to the metals’s high mobility [131. Thus a maximum concentration of 3570 pg Zn g- ’ is found on a terrace adjacent to the mine dump which is partly irrigated with mine waste water. This dispersion of Zn contributes to the enhancement of Zn in paddy soils (> 500 pg Zn g-’ ) in
108
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Table 1 The physical and chemical properties of paddy soil samples along six traverse lines in the Sambo Pb-Zn mine Before planting rice Depth
CEC beq/ lOOg, Sand (%I Silt (%I Clay (%I
N
Range
5.sa 4.ga
4.0-6.9 4.3-5.3
O-15
PH LOI (%)
Mean
IS-30 30-45 o-15 15-30 30-45
-
4.7a 3.5a
-
o-15 15-30
2.2-9.8 2.6-4.2 -
7.9= 8.2a
30-45
-
o-15 15-30
ND ND -
30-45 o-15 15-30 30-45 n-15 15-30 30-45
ND ND ND ND
o-15 15-30
34 5 0
30-45
6.2-9.9 7.0-9.1
ND ND ND ND ND ND 14 14 14
After 30 days Mean Range 5.5" 5.5" 5.6" 5.4a 5.0b 4.6a 13.2b 12.2b 11.9a 71.9a 75.4a 74.6= 21.7a 14.6a 14.6a 6.5a
4.6-6.5 5.0-6.0 5.0-6.4 3.4-7.5 3.6-7.2 2.5-7.6 7.6-16.6 8.7-16.1 8.6-16.9 67.5-77.0 72.8-78.0 70.0-82.0 14.4-29.3 9.0-12.0 10.0-19s 2.5-12.1 9.0-12.0 8.0-13.0 31 31 31
10.Y ll.oa 31 31 31
After 80 days Mean Range 5.5b 5.4b 5.8b 4.7b 4.6' 4.2b 11.3c 11.2c
4.6-6.5 4.8-6.4 4.8-6.7 3.1-6.4 3.1-6.2 2.0-5.9 7.9-15.1 8.2-15.0 8.1-13.7 68.5-84.9 67.8-77.7 68.0-83.0 9.0-28.5 20.0-27.2 10.8-29.3 3.0-12.2 2.2-7.2 2.2-6.2
10.8b 75.3" 73.8a 75.5= 16.2a 21.9b 20.2b 8.5a 4.3b 4.3b
After 150 days Mean Range 5.3* 5.4a 5.4a 5.2c 4.6d 4.3c 11.3d
10.8d 10.8a 75.4a 76.0a 72.6a 15.0a
15.1C 17.V 9.5a 8.9' 10.4a
4.8-6.4 4.6-6.2 4.8-6.3 3.5-7.3 3.0-6.7 2.5-6.2 7.7-14.3 8.1-13.7 8.3-14.3 70.0-82.0 71.0-81.5 68.7-76.0
11.5-17.5 1X3-20.7 15.0-19.0 6.2-13.0 7.2-10.2 8.0-13.0
ND, not determined; -, no sample taken; azbSignificant difference in adjacent column (the time of sampling) of the same row (soil properties) at P < 0.05. Table 2 Mean concentrations and ranges of Cd, Cu, Pb and Zn in paddy soils sampled along six traverse lines in the Sambo Pb-Zn mine (/+I g-‘) Before planting rice Depth Cd
CU
Pb
Mean
O-15 15-30 30-4s O--l5 15-30 30-45
Range
1.7a
0.6-7.3
0.9"
0.8-1.1 < l-103 15-16 17-408
31 16
O-15 15-30
After 30 days
90 25
20-29
30-4s Zn
N
o-15 15-30
465
30-4s O-1 15-30 30-45
--
188 34 5 0
74-3100 114-379
14 14 14
Mean 1.3a 0.9a 0.9a 35a 28a 28a 84a 79" 79a 627" 134a 345a 31 31 31
After 80 days Range
0.3-5.8 0.2-3.2 0.2-2.7 21-78 14-59 15-63 24-318 23-327 21-361 101-35x 76-1820 76-1460 31 31 31
Mean 1.3" 1.7b
l.oa 33a 34* 28a 85a 1198 78a 507a 656a 442a
Range 0.3-4.3 0.3-7.8 < 0.2-3.2 15-84 12-77 13-62 21-319 21-483
11-411 58-1880 56-3350 56-1480
After 150 days Mean Range 1.6a 1.3a 1.2a 32' 29a 27a 114a 94a 85a 681a 504a 450a
0.3-4.8 0.2-3.9 0.2-3.9 12-77 12-68 12-77 19-483 17-406 16-490 51-3350 52-2180 51-1860
net sample taken. ’ ” Significant difference in adjacent column (the time of sampling) of the same row (metal concentration in soil) at P < 0.05.
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Table 3 The physical and chemical properties and metal concentrations in irrigation waters sampled along six traverse lines in the vicinity of the Sambo Pb-Zn mine After 30 days (N = 14) Cd(figl-‘) cu(~gl-‘) PbtFgI-*) Zn(pgl-‘) Temperature (“0 PH Eh (rnv)
AM
GM
7.Y 9.6a 20.4a 4580a 19.Sa 6.6a 226a
3.7 5.3 14.4 218
After 80 days (N = 31) GM AM
Range 1.0-50.0 1.0-53.0 1.0-67.0 1.0-49 100 18.2-21.3 5.5-7.4 160-296
4.3b 8.5b 12.0b 486b 23.4b 6.8a 240’
Range
3.6 4.1 9.6 60.9
1.0-9.0 1.0-35.0 2.0-35.0 20-8510 21.8-24.6 6.2-7.3 42-368
N, numbers of sample; AM, arithmetic mean; GM, geometric mean. “.bSignificant difference in adjacent column (the time of sampling) for arithmetic mean of the same row (metal concentration and some properties) at P < 0.05..
comparison with those from the control site (< 100 pg Zn g-l). Concentrations of Cd, Cu, Pb and Zn in irrigation waters are summarised in Table 3. Because a large amount of water is needed in the early stage of rice growing, it is inevitable that large quantities of mine waste water will be used in the paddy fields around the vicinity of the mine. Thus, some irrigation waters sampled at 30 days after transplanting contain high concentrations of metals. A wide range of Cd concentrations of 1.0-50 pg 1-l is found, with high levels from the vicinity of the mine (> 10 pg 1-l) and low concentrations from the control site. Concentrations of Cu are similar, ranging from 1.0 to 53 pg 1-l. In spite of the high concentrations of Pb in soils from the mining
area (41-29900 pg g-i) [13], relatively low Pb concentrations are found in irrigation waters of < 67 pg 1-i due to its very low solubility. However, Zn concentrations are high, ranging up to 49100 pg Zn 1-i. It can be expected that such high concentrations of Zn may influence both the composition of paddy soils and metal uptake into rice grain and stalk.1 3 Mean concentrations and ranges of metals in rice stalk and grain samples are shown in Table 4. Concentrations of Cd range from 0.1 to 5.0 pug g-i (dry wt.) in rice stalks and leaves, and from 0.1 to 0.5 /J,g g -I (dry wt.) in grain. It has been reported that Cd concentrations in rice stalk grown on soils developed from cadmium-rich black shale in Korea averaged 1.7 pg g-i (dry
Table 4 Mean concentrations and ranges of Cd, Cu, Pb and Zn in rice stalks and grain sampled along six traverse lines in the vicinity of the Sambo Pb-Zn mine ( pg g-l, dry weight) Rice stalks
Rice grain
After 30 days Mean Cd cu Pb Zn N
0.35a 10.4” 4.9” 95” 14
After 80 days Range
Mean
Range
0.20-0.70 5.3-22.6 3.1-10.3 27-486 31
0.46” 9.5a 2.ga 74” 31
0.20-1.50 4.6-20.4 1.6-8.8 24-415 31
After 150 days
After 150 days Mean 0.77b 9.7a 5.8b 137b
Range 0.10-5.00 6.1-20.1 3.0-16.9 20-471
Mean 0.21C 3.0a 0.2za 25.2a
,
Range 0.10-0.50 1.2-5.8 < 0.1-0.6 19.0-37.0
“bSignticant difference in adjacent column (the time of sampling) of the same row (metal concentration in rice stalk) at P < 0.05. N, numbers of sample.
110
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Jung, I. Thornton
/The
Science
wt.), ranging from 0.1 to 6.6 pg g-’ (dry wt.) and 0.6 pug g-’ (dry wt.) with a range of 0.1-3.5 pg g-’ (dry wt.> in rice grain 181. Watanabe et al. (1989) reported that the geometric mean Cd in worldwide rice grain (n = 207) was 0.02 pg g-’ (dry wt.); they also reported that Cd levels in Korean rice grain averaging 0.016 pg gg’ (dry wt.), with a range of 0.006-0.045 pg g-’ (dry wt.) [5]. In comparison with their data, rice grain in the present study contains about 20 times greater Cd levels. Copper concentrations in rice stalk and leaf range from 9.5 to 10.4 pg g-’ (dry wt.> and in rice grain from 1.2 to 5.8 ,ug gg’ (dry wt.) (Table 41. According to Masironi et al. (1977) [4], worldwide Cu concentrations in rice grain (n = 100) average 4.0 pg g -’ (dry wt.) (unpolished) and 3.0 pg g-’ (dry wt.) (polished). Lidon and Henriques (19921 reported a Cu toxicity when rice contained 35.1 pug g-’ (dry wt.> 1171. With the exception of some rice stalk (> 15 pg g-‘, dry wt.), most samples have relatively low Pb concentrations, ranging from 2.8 to 5.8 pg g-’ (dry wt.> (Table 4). Watanabe et al. (1989) reported a worldwide geometric mean value of 0.016 pg gg ’ (dry wt.) in rice grain, with a range of 0.004-0.032 pg g-’ (dry wt.) [5]. They also found that Pb in Korean rice grain averaged 0.012 pg gg ’ (dry wt.), with a range of 0.004-0.032 pg g-’ (dry wt.). In comparison with their data, rice grain samples reported here ( < 0.1-0.6 pg g-‘, dry wt.) contain about 20 times higher Pb levels. Zinc concentrations in rice samples range from 74 to 137 pg g-’ (dry wt.) in the stalk samples and from 19 to 37 pg gg’ (dry wt.) in the grain samples, which are higher than worldwide Zn concentrations of 16.4 pg g-’ (dry wt.) (unpolished) and of 13.7 pg g-’ (dry wt.) (polished) reported by Masironi et al. (19771 [4]. High concentrations of Zn in the rice samples are strongly influenced not only by those in the paddy soils and irrigation waters but also the high bioavailability of Zn to plants. S..?. Seasonal variation Many workers have found increasing soil pH under submerged conditions, especially in acid soils [3,10,18]. When paddy soils are flooded, the
of the
Total Enuironment
I98 (1997) 105-121
diffusion of 0, into the soils and CO, out of the soil is greatly restricted, resulting in the accumulation of CO, [11,12]. This increases the concentrations of HCO; and CO:- in the soil solution and may cause elevation of soil pH and precipitation of metals. Although variation is found between sampling sites, surface soil pH under reducing conditions (30 and 80 days after transplanting rice) is higher than that under oxidising conditions (150 days after) (Fig. 1). Statistically significant difference in soil pH is found between 80 and 150 days after planting the rice (P < 0.05) (Table 1). Thus the soil pH generally decreases in the order: 80 days 2 30 days > 150 days after planting. Similar results are also found in the subsurface soils (15-45 cm depth). The organic matter content of surface soils, measured by losson-ignition, shows that soils sampled at 80 days have lower organic matter contents than those at 30 and 150 days after (P < 0.05) (Fig. 1). Similar results are also found in subsurface soils (Table 1). The seasonal variation in cation exchange capacity of surface soils is similar to that in organic matter. There is little seasonal variation in water pH and Eh. However, a relatively high water temperature is found at 80 days after rice transplanting (P < 0.05) due to an increase in the air temperature during August (Table 3). There is little variation in metal concentrations in paddy soils throughout the period of rice growing (Fig. 2). In the highly contaminated soils, however, soils taken at 30 and 150 days contain higher metal contents that those at 80 days after. Relatively high metal concentrations are found in irrigation waters sampled at 30 days compared with 80 days (P < 0.05) (Table 3). These elevated levels of metals may be derived directly from the mine waste water and from rain water that has infiltrated and passed through the mine dumps. Seasonal variation of metal concentrations in rice stalk is presented in Fig. 3. The figure shows that rice stalks and leaves sampled at 30 days and 150 days after transplanting contain higher metal concentrations than those sampled at 80 days (P < 0.05). Relatively low metal concentrations in rice growing under reducing conditions may be due to their precipitated as hydroxide, carbonates, sulphide and iron compounds [3,9,12].
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111
105-121
q 0
I
u 11
8
6O
I 1
2
3
4
5
6
7
8
q
9
I
m
I 10
11
12
13
14
Site numb4x-s m 30 days after
0
8Odaysaiter
0
150 days after
Fig. 1. Seasonal variations in soil pH, loss-on-ignition and cation exchange capacity of surface soils (O-15 cm depth).
3.4. Relationships between metal concentrations in soils, rice and water
Relationships between metal concentrations in rice stalks and surface soils are shown in Fig. 4. From the figure, it can be seen that metal concentrations in rice stalks increase with increasing levels in surface soils (P < 0.001). The rate of increase of metals in rice stalks differs from metal to metals, higher rates for Cd and Zn and lower rates for Cu and Pb. This is assumed to be due to
differences in the solubility and bioavailability of these metals. Positive correlations between metal concentrations in rice grain and surface soil are also found (P < 0.001) (Fig. 5). Significant correlations are also found between metal concentrations in rice stalks and grain (Fig. 6). 3.5. Factors affecting metal uptake by rice
Many researchers have investigated factors influencing metal uptake by rice. These factors included soil pH [10,12,19], redox potential [11,18],
M.C. Jung, I. Thornton /The Science of the Total Environment 198 (1997) 105-121
112
of most important factors affecting metal bioavailability is soil pH. A relatively low metal
organic matter content 120,211, phosphorous content 122,231, temperature [24] and time 1251. One
.Ei a
1. 10 -;0
,
I 1
2
3
4
I 5
6
7
8
9
10
I 12
11
, 13
Site numbers cl
/ m30daysaik c
Fig. 2. Seasonal variations in
metal
80daysafter
G
150days
concentrations of surface soils (O-15
after
cm depth).
14
M.C. Jung, I. Thornton /The Science of the Total Environment 198 (1997) 105-121
113
0 0
0.6
Ef
O
0
q m
0 0
m 0.3
0.0
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,
I
I
I
1
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0
6 0
lo’ , 0 1
0
X
0
0
0
0
0
0” B
8 m
m30daysatIer
3
4
0
0
m 0
I 2
0
M
m 0 0
m
0
I 5 0
I 1 6 7 8 9 Site numbers 80days&er
0 •El
m q 0
! 10 0
11
12
/ 13
14
150daysafter
I
I
Fig. 3. Seasonal variations in metal concentrations of rice stalks and leaves.
uptake by rice was found under reducing condition due to increasing soil pH [lo]. This study also
shown that metal concentrations in rice stalks growing under reducing conditions are lower than
114
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/The
Science of the Total Enuironment
198 (I997)
105121
Cd in surfacesoil (jg/g)
Y = 2.30 + 0.0177 X (r = 0.75**‘)
F%in sufece soil (rs/g) 500E
Y=22.1 +0.134x(r=o.90*“)
500
1000
1500
2000
2500
3000
3500
2% in Lwrfece soil (18/g) l
**
Significant at p < 0.001
Fig. 4. Relationships between metal concentrations in surface soils (O-15 cm depth) and rice stalks.
those growing under oxidising conditions (see Fig. 3). Many studies found that an increase in soil
organic matter content increases the exchangeable Fe and Mn in soils under flooded conditions
M.C. Jung, I. Thornton
/The
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198 (1997)
115
10512I
Cd ia surfacesoil (B/S)
i!O i!o
sb
$0
$0
Cu in surfacesoil (jg/g) Y = 0.0961 + 0.00137X (r = 0.89***)
s q 0.7-
. .
C?
, 50
I 100 I
/ 150
II 200
/
l
**
II 250
II 300
II 350
II 400
II 450
J
Zn in surfacesoil (@g/p) Sigaificantat p
Fig. 5. Relationships between metal concentrations in surface soils (O-15 cm depth) and rice grain.
and decreases the availability of metals to plants [20,21,26]. Because little variation exists in the
organic matter content and cation exchange capacity of soils, no significant relationships are
116
M.C. Jung, I. Thornton / The Science of the Total Environment 198 (1997) 105-121
is cl 0s
Y=O.1SO+O.llOX(r=0.87***)
Cdinricestalk(jg/g,DW)
.
I 10
I a
I 12
I 14
.
.
I 16
I ia
20
Cuinricoaralk(IO/8,Dw) g
OB-
Y=-O.O573
+0.0681X(r=0.78***)
.
/
I .
2.0
3.0
I 4.0
I 5.0
I 6.0
I 7.0
.
T a.0
Pbinriccatdk(Jg/8,Dw) . 5 9
Y=20.7+0.0414X(r=0.89***) 40-
,
50
100
150
200 l
250
300
350
400
450
500
Zn in rice stalk (re/g, DW) ** Si8nifiomt at p < 0.001
Fig. 6. Relationships between metal concentrations in rice stalks and grain.
M.C.
Jung, I. Tbmton
/ The Science of the Total Enuironment
found in this study. However, it is concluded ideally that high metal uptake by rice of the paddy soils in this study will be influenced by the low organic matter contents and cation exchange capacity. 3.6. Chemical speciation of paddy soils
Although the total metal concentrations in paddy soils have been shown to influence metal concentrations in rice, the chemical forms of metals in the soils will also affect metal uptake by rice. Many workers have investigated metal speciation and bioavailability in paddy soils using a sequential extraction scheme [27-301. This study has been also applied in this under both reducing and oxidising soil conditions [31]. The results of sequentially extracted metal concentration in selected samples are shown in Fig. 7 and partitioning of the metals in each fraction is presented in Fig. 8. The selected samples were taken sites f‘Rl-SO’ and ‘Rl-150’, ‘R2-80’ and ‘R2-150’ and ‘R3-80’ and ‘R3-150’ at 80 days and 150 days after transplanting, respectively. Under submerged conditions (sample identifications ‘Rl-80’, ‘R2-80 and ‘R3-80’1, Cd and Zn in the soils is largely associated with the Fe and Mn oxide fraction and, to a lesser extent, the carbonate and specifically adsorbed fractions. It has been found that Zn present in amorphous sesquioxide-bound and exchangeable bound forms contributed to Zn uptake by rice [281. Under oxidising conditions (sample identifications ‘R2-150’ and X3-150’), relatively low concentrations of Cd, Pb and Zn are presented in the Fe and Mn oxide fraction, with the exception of sample ‘Rl-80’. In comparison, under reducing conditions, relatively high concentrations of metals are found in the exchangeable fraction, due possibly to the dissolution of metals presented in the Fe and Mn oxides. This result is in agreement with the fact that metal concentrations in rice growing under oxidising conditions are higher than those under reducing conditions. Throughout the period of rice growing, under both flooded and unllooded conditions, there is no significant seasonal variations of metals pre-
I98 (I997)
105-12~
117
sent in the carbonate, organic and residual fractions. 3.7. Implication
to animal and human health
Soils contaminated by various sources may influence the composition of food crops, and the proportion of different crops in the diet may affect the total metal intake by grazing animals. In the study area, cattle and swine are reared on small farms. The common diet of these animals is normally locally grown crops with rice stalks for cattle and corn for swine. As shown in Table 4, metal concentrations in rice stalks and leaves are significantly elevated. These metals can then be directly ingested by cattle. Because rice stalks and leaves are fed to cattle without washing, livestock can also ingest metals in soils adhering to their surface. It was not possible to sample animal tissue from the study area due to lack of resources, however, it is likely that animals in the study area will ingest metals through a diet grown on soils contaminated by the mining activity. Human health may be affected by the amount of chemical elements ingested and inhaled via food, drinking water and atmosphere [32]. The dietary intake of cereal (mainly rice) by Koreans is estimated to be 574 gram per day [3]. The average Cd concentration in rice grain grown in the study area is 0.21 pg g-i (dry wt.). In general, the residents in the study area consume crop plants grown in their own rice fields. When the residents regularly consume rice, the average daily intake of Cd from the rice is up to 120.5 pg (= 574 g day-’ x 0.21 pg g- ‘). This figure markedly exceeds the provisional tolerable weekly intake (PTWI) of 400-500 pg Cd recommended by the FAO and WHO [33]. The average daily intake of Pb intake from the rice by the residents is estimated to be 126 pg (= 574 g day-’ X 0.22 lug g-i), with a range of < 57.4-344 pg; this is about 30% of provisional daily intake of 430 pg recommended by the FAO and WHO [33]. Although human health studies have not been undertaken, regular consumption of the rice by the residents in the study area poses a potential health problem from long-term metal exposure, espe-
Rl-150
IL?-80
R2-150
R3-80 I&150
200
1
5o 0
* 150 r=: 2 100 .5
3
0.5 0
RI-80
R2-80
R2-150
R3-80
Bound onto carbonate Residual fhction
R3-150
0
R1-80
Rl-80
R2-80
Ft2-80
R2-150
RI-150
R3-80
R3-80
Bound onto Fe & Mn oxides
Rl-150
Rl-150
Fig. 7. Diagrams of sequentially extracted metal concentrations in selected paddy soils.
Exchangeable fraction Bound onto organic matter
RI-150
u
.5 10 k op
2 4
Rl-80
4 $j 20
0
30
i
‘;; 2.5
.7J 2 .z 1.5
l
40
-
#- 3.53
R3-150
R3-150
M.C. Jung, I. Thornton
/ T Fze Scienc :e of the Total Environment
19, 9 0997)
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119
120
M.C. Jung, I. Thornton /The Science of the Total Environment 198 (1997) 105-121
cially for Cd and Pb and to a lesser extent for Cu and Zn. 4. Conclusions
The physical and chemical properties of paddy soils sampled along six traverse lines around the mine were similar to those reported for Korean soils, with the exception of some soils sampled in the immediate vicinity of the mine which were characterised by low pH, organic matter content, cation exchange capacity and high proportions of sand. Concentrations of Cd, Cu, Pb and Zn in paddy soils and irrigation waters sampled in the vicinity of the mine were higher than those sampled in the control area due to the influence of effluent of metals from mine dump materials. Elevated levels of the metals were also found in rice stalks, leaves and grain taken around the mining area. Although there were variations between sampling sites, soil pH values under reducing soil conditions were higher than those under oxidising conditions (P < 0.051. Statistical differences between 80 days after and 30 days and 150 days after rice transplanting were found in loss-onignition and cation exchange capacity 0’ < 0.05). However, there is little seasonal variation in irrigation water pH and Eh values, and metal concentrations in paddy soils throughout the period of rice growing. This study found that metal concentrations in rice stalks and leaves sampled at 30 days and 150 days after transplanting were relatively higher than those sampled at 80 days (P < 0.051. This result was supported by results from the sequential extraction analysis of selected samples; in comparison with reducing conditions, higher proportions of exchangeable meta fractions was found under oxidising conditions (harvest season). Metal concentrations in rice stalks and leaves increased with increasing metal contents in surface soils (P < 0.001) and the rate of increase of metals in the rice varied from metal to metal, with higher rates for Cd and Zn and lower rates for Cu and Pb due to differences in solubility and bioavailability. Positive correlation of metal concentrations in rice grain and in surface soils (P <
O.OOl), and in rice stalks and leaves and grain (P < 0.001) were also found. Unwashed rice stalks and leaves are an important source of heavy metal intakeby some livestock, especially swine and cattle reared on the small farms around the mine. In addition, The residents living near the mine regularly consume the rice grown on soils contaminated by the mine. The average metal intake from the rice by these residents was estimated to be 120.5 pg day-’ of Cd, which markedly exceeds the guideline of Cd intake recommended by the FAO and the WHO and 126 lug day-i of Pb, which are about 30% of provisional tolerable daily intake of 430 pg recommended by FAO and the WHO 1331. Thus, long-term metal exposure by regular consumption of locally grown vegetables and rice poses potential health problems to residents in the vicinity of the mine, although no adverse health effects have as yet been observed. References Ul MS. Kim, Soils of Korea and their improvement.
Agri-
cultural Science Institute Rural Development Administration, Suwon, Korea, 1985. PI Europa World Year Book, The Europa World Year Book, Europa Publications, 1992. [31 K. Kitagishi and I. Yamane, Heavy metal pollution in soils of Japan. Japan Scientific Societies Press, Tokyo, 1981. [41 R. Masironi, S.R. Koirtyohann and J.O. Pierce, Zinc, copper, cadmium and chromium in the polished and unpolished rice. Sci. Tot. Environ., 7 (1977) 23-43. [51 T. Watanabe, H. Nakatsuka and M. Ikeda, Cadmium and lead in rice available in various areas of Asia. Sci. Tot. Environ., 80 (1989) 175-184. 161 J.C. Fernandes and F.S. Henriques, Heavy metal contents of paddy fields of Alcacer Do Sal, Portugal. Sci. Tot. Environ., 90 (1990) 89-97. PI Z.-S. Chen, Cadmium and lead contamination of soils near plastic stabilizing materials plants in northern Taiwan. Water, Air, Soil Pollut., 57-58 (1991) 745-754. is1 K.W. Kim, and I. Thornton, Influence of uraniferous black shales on cadmium, molybdenum and selenium in soils and crop plants in the Deog-Pyong area of Korea. Environ. Geochem. Health, 15 (1933) 119-133. [91 F.T. Bingham, A.L. Page, R.J. MahIer and T.J. Game, Cadmium availability to rice in sludge-amended soil under ‘flood’ and ‘nonflood’ culture. Soil Sci. Sot. Am. J., 40 (1976) 715-719.
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Jung, I. Thornton
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Science of the Total Environment
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[141
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iI61
1171
Ml
[191
[201
m
potential and pH on the uptake of cadmium and lead by rice plants. J. Environ. Qual., 6 (1977) 259-262. KS. Sajwan and W.L. Lindsay, Effects of redox on zinc deficiency in paddy rice. Soil Sci. Sot. Am. J., 50 (1986) 1264-1269. D. Dutta, B. Mandal and L.N. Mandal, Decrease in availability of zinc and copper in acidic to near neutral soil on submergence. Soil Sci., 147 (1989) 187-195. M.C. Jung and I. Thornton, Heavy metal contamination of soils and plants in the vicinity of a lead-zinc mine, Korea. Appl. Geochem., 11 (1996) 53-59. M. Thompson and J.N. Walsh, A handbook of Inductively Coupled Plasma Atomic Emission Spectrometty, 2nd edn, Blackie, London, 1988. M. Thompson, M.H. Ramsey and B. Pahlavanpour, Water analysis by inductively coupled plasma atomic emission spectrometry after a rapid pre-concentration. Analyst, 107 (1982) 1330-1334. M.H. Ramsey, M. Thompson and E.K. Banerjee, Realistic assessment of analytical data quality from inductively coupled plasma atomic emission spectrometry. Anal. Pm., 24 (1987) 260-265. F.C. Lidon and F.S. Henriques, Copper toxicity in rice: diagnostic criteria and effect on tissue Mn and Fe. Soil Sci., 154 (1982) 130-135. J.W.O. Jeffery, Detining the status of reduction of a paddy soil. J. Soil Sci., 12 (1961) 173-179. F.T. Bingham, A.L. Page and J.E. Strong, Yield and cadmium content of rice gram in relation to addition rates of cadmium, copper, nickel, and zinc with sewage sludge and liming. Soil Sci., 130 (1980) 32-38. M. Haldal and L.N. Mandal, Influence of soil moisture regimes and organic matter application on the extractable Zn and Cu content in rice soils. Plant Soil, 53 (1979) 203-213. A. Swarup, Influence of organic matter and flooding on the chemical and electrochemical properties of sodic soil and rice growth. Plant Soil, 106 (1988) 135-141.
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L.N. Mandal and M. Haldar, Influence of phosphorus and zinc application on the availability of zinc, copper, iron, manganese and phosphorus in waterlogged rice soils. Soil Sci., 130 (1980) 251-257. Bl M. Haldar and L.N. Mandal, Effect of phosphorus and zinc on the growth and phosphorus, zinc, copper, iron and manganese nutrition of rice. Plant Soil, 59 (1981) 415-425. WI D.Y. Cho and F.N. Ponnamperuma, Influence of soil temperature on the chemical kinetics of flooded soils and growth of rice. Soil Sci., 119 (1971) 184-194. [251 G.T. Gilmour, Micronutrient status of the rice plant: I. plant and soil solution concentrations as a function of time. Plant Soil, 46 (1977) 549-557. WI B. Mandal, G.C. Hazra and A.K. Pal, Transformation of zinc in soils under submerged condition and its relation with zinc nutrition of rice. Plant Soil, 106 (1988) 121-126. WI A.S.P. Murthy, Zinc fractions in wetland rice soils and their availability to rice. Soil Sci., 133 (1982) 150-154. [281 M.V. Singh and I.P. Abrol, Transformation and movement of zinc in an alkali soil and their influence on the yield and uptake of zinc by rice and wheat crops. Plant Soil, 94 (1986) 445-449. 1291G.C. Hazra, B. Mandal and L.N. Mandal, Distribution of zinc fractions and transformation in submerged rice soils. Plant Soil, 104 (1987) 175-181. [301 L.N. Mandal and B. Mandal, Transformation of zinc fractions in rice soils. Soil Sci., 143 (19871 205-212. [311 X. Li, B.J. Coles, M.H. Ramsey and I. Thornton, Sequential extraction of soils for multielement analysis by ICP-AES. Chem. Geol., 124 (1985) 109-123. WI S.H.U. Bowie and I. Thornton, Environmental Geochemistry and Health. D. Reidel Publishing Co., Holland, 1984. [331 WHO, Guidelines for Drinking-water Quality. vol. 1 recommendations. 2nd edn. WHO, Geneva, 1993. t221