Bioavailability to grains of rice of aged and fresh DDD and DDE in soils

DDT had been widely used around the world before 1980s and is still under production and use for non-agricultural purposes in China. Because of their special physicochemical properties, p,p'-DDT and its main metabolites, p,p'-DDD and p,p'-DDE, accumulated and persisted in the environment, presenting potential menace on biota. A green-house study was conducted to determine the bioavailability of p,p'-DDD and p,p'-DDE to grains of rice and the influences of traditional Chinese farming practices on their bioaccumulation. Paddy rice and dry rice were grown in submerged paddy soils and non-submerged upland soils, respectively. Two types of soil, Hydragric Anthrosols (An) and Hydragric Acrisols (Ac), were employed. Bioaccumulation factors (BAFs) of DDE ranged from 0.67 for rice grown in non-submerged An to 0.84 in submerged An in the control group, whilst BAFs were all below 0.04 in experimental groups. BAFs of DDD varied from 1.39 for submerged An to 2.26 for submerged Ac in original soils. In contrast, BAFs were between 0.05 for non-submerged Ac and 0.08 for submerged An in DDD-contaminated soils. Flooding seemed to have two contradictory effects on the DDE/DDD accumulation by rice: on one hand, it made the pollutants more mobile and bioavailable; while on the other hand, it enhanced the degradation and binding of POPs. Adding rice straw to the soils protected DDE from being taken up yet promoted DDD accumulation by rice. Furthermore, the distinct inorganic component of the soils might also play an important role in the environmental activities of POPs.     

Adsorption of arsenate on soils. Part 2: modeling the relationship between adsorption capacity and soil physiochemical properties using 16 Chinese soils

An attempt has been made to elucidate the effects of soil properties on arsenate adsorption by modeling the relationships between adsorption capacity and the properties of 16 Chinese soils. The model produced was validated against three Australian and three American soils. The results showed that nearly 93.8% of the variability in arsenate adsorption on the low-energy surface could be described by citrate-dithionite extractable Fe (Fe(CD)), clay content, organic matter content (OM) and dissolved organic carbon (DOC); nearly 87.6% of the variability in arsenate adsorption on the high-energy surface could be described by Fe(CD), DOC and total arsenic in soils. Fe(CD) exhibited the most important positive influence on arsenate adsorption. Oxalate extractable Al (Al(OX)), citrate-dithionite extractable Al (Al(CD)), extractable P and soil pH appeared relatively unimportant for adsorption of arsenate by soils.     

Effects of compost, pig slurry and lime on trace element solubility and toxicity in two soils differently affected by mining activities

The use of organic wastes as amendments in heavy metal-polluted soils is an ecological integrated option for their recycling. The potential use of alperujo (solid olive-mill waste) compost and pig slurry in phytoremediation strategies has been studied, evaluating their short-term effects on soil health. An aerobic incubation experiment was carried out using an acid mine spoil based soil and a low OM soil from the mining area of La Unión (Murcia, Spain). Arsenic and heavy metal solubility in amended and non-amended soils, and microbial parameters were evaluated and related to a phytotoxicity test. The organic amendments provoked an enlargement of the microbial community (compost increased biomass-C from non detected values to 35 μg g⁻¹ in the mine spoil soil, and doubled control values in the low OM soil) and an intensification of its activity (including a twofold increase in nitrification), and significantly enhanced seed germination (increased cress germination by 25% in the mine spoil soil). Organic amendments increased Zn and Pb EDTA-extractable concentrations, and raised As solubility due to the influence of factors such as pH changes, phosphate concentration, and the nature of the organic matter of the amendments. Compost, thanks to the greater persistence of its organic matter in soil, could be recommended for its use in (phyto)stabilisation strategies. However, pig slurry boosted inorganic N content and did not significantly enhance As extractability in soil, so its use could be specifically recommended in As polluted soils.     

Adsorption and absorption of dichlorodiphenyltrichloroethane (DDT) and metabolites (DDD and DDE) by rice roots

A three-step sequential extraction procedure was applied to measure the concentrations of dichlorodiphenyltrichloroethane (DDT) on rice root surface and in root tissues collected from two sites in Tianjin. Bulk and rhizosphere soils were also analyzed. The measured DDXs in the rhizosphere soils were significantly higher than those in the bulk soils. On average, p,p'-DDT, p,p'-DDD, and p,p'-DDE in the soil accounted for 38%, 47% and 15% of the total. For total DDXs, approximately one third remained on the outer surface of the roots. The partition of DDXs between rhizosphere soil and root surface depend on contaminant affinity to soil organic matter, soil organic matter content and root specific area. A case specific equation was developed to quantitatively describe the partition of DDXs between soil and root surface.     

Chemical speciation and extractability of Zn,Cu and Cd in two contrasting biosolids-amended clay soils

An incubation experiment was conducted to study the chemical speciation and extractability of three heavy metals in two contrasting biosolids-amended clay soils. One was a paddy soil of pH 7.8 and the other was a red soil of pH 4.7 collected from a fallow field. Anaerobically digested biosolids were mixed with each of the two soils at three rates: 20, 40 and 60 g kg(-1) soil (DM basis), and unamended controls were also prepared. The biosolids-amended and control soils were incubated at 70% of water holding capacity at 25 degrees C for 50 days. Separate subsamples were extracted with three single extractants and a three-step sequential extraction procedure representing acetic acid (HOAc)-soluble, reducible and oxidisable fractions to investigate the extractability and speciation of the heavy metals. As would be expected, there were good relationships between biosolids application rate and metal concentrations in the biosolids-amended soils. The three heavy metals had different extractabilities and chemical speciation in the two biosolids-amended soils. Ethylene diamine tetraacetic acid extracted more Cu, Zn and Cd than did the other two single extractants. The oxidisable fraction was the major fraction for Cu in both biosolids-amended soils and the HOAc-soluble and reducible fractions accounted for most of the Zn. In contrast, Cd was present mainly in the reducible fraction. The results are discussed in relation to the mobility and bioavailability of the metals in polluted soils.     

CH4 and N2O emissions from Spartina alterniflora and Phragmites australis in experimental mesocosms

Spartina alterniflora, a perennial grass with C(4)-photosynthesis, shows great invading potential in the coastal ecosystems in the east of China. We compared trace gas emissions from S. alterniflora with those from a native C(3) plant, Phragmites australis, by establishing brackish marsh mesocosms to experimentally assess the effects of plant species (S. alterniflora vs. P. australis), flooding status (submerged vs. non-submerged), and clipping (plants clipped or not) on trace gas emissions. The results show that trace gas emission rates were higher in S. alterniflora than P. australis mesocosms due to the higher biomass and density of the former, which could fix more available substrates to the soil and potentially emit more trace gases. Meanwhile, trace gas emission rates were higher in non-submerged than submerged soils, suggesting that water might act as a diffusion barrier in the brackish marsh mesocosms. Interestingly, methane (CH(4)) emission rates were lower in clipped non-submerged mesocosms than in non-clipped submerged mesocosms, but nitrous oxide (N(2)O) emissions were enhanced. CH(4) emissions were significantly correlated with the plant biomass and stem density (R(2)>0.48, P<0.05) for both species, suggesting that both the two species might play important roles in CH(4) production and transport and also act as suppliers of easily available substrates for the methanogenic bacteria in wetland ecosystems. N(2)O emissions, however, were not significantly correlated with plant biomass and density (P>0.05).     

Cadmium (Cd) distribution and contamination in Chinese paddy soils on national scale

Rice is a staple food by an increasing number of people in China. As more issues have arisen in China due to rice contaminated by cadmium (Cd), Cd contamination in arable soils has become a severe problem. In China, many studies have examined Cd contamination in arable soils on a national scale, but little studies have focused on the distribution of Cd in paddy fields. This study explored the spatial pattern of Cd in paddy soils in China, made a preliminary evaluation of the potential risk, and identified the most critically contaminated regions based on the domestic rough rice trade flow. The results showed that Cd concentrations in paddy soils in China ranged from 0.01 to 5.50 mg/kg, with a median value of 0.23 mg/kg. On average, the highest Cd concentrations were in Hunan (0.73 mg/kg), Guangxi (0.70 mg/kg), and Sichuan (0.46 mg/kg) provinces. Cd concentrations in paddy soils in central and western regions were higher than those in eastern regions, especially the southeastern coastal regions. Of the administrative regions, Cd standard exceedance rate was 33.2 %, and the heavy pollution rate was 8.6 %. Regarding to Cd of paddy soil, soil environmental quality was better in Northeast China Plain than in Yangtze River Basin and southeastern coastal region. Mining activities were the main anthropogenic pollution source of Cd in Chinese paddy soil. Based on rice trade, more of the Chinese population would be exposed to Cd through intake of rice produced in Hunan province. Certain regions that output rice, especially Hunan province, should be given priority in the management and control of Cd contamination in paddy soil.     

Influence of ozonation on extractability of Pb and Zn from contaminated soils

The effect of soil ozonation on Pb and Zn extraction with EDTA, bioavailability (Ruby's Physiologically Based Extraction Test, PBET) and mobility (Toxicity Characteristic Leaching Procedure, TCLP) of Pb was studied on contaminated soils taken from 7 different locations in the Mezica Valley, Slovenia. EDTA extraction (40 mmol kg(-1)) removed from 27.4+/-1.5% to 64.8+/-1.5% of Pb, and from 1.9+/-0.2% to 22.4+/-2.0% of Zn from tested soils, and significantly reduced soil Pb bioavailability (PBET) and mobility (TCLP). Pretreatment of tested soils with ozone before EDTA extraction enhanced EDTA extractability of Pb for 11.0 to 28.9%, but had no effect on the extractability of Zn. In most of the soils, ozonation had no statistically significant effect on bioavailability and mobility of Pb, residual after EDTA extraction. Using linear regression analysis we found a significant increase (p<0.01) in EDTA extractability of Pb after soil ozonation in soils with a higher initial Pb content. EDTA extractability of Pb after soil ozonation was also significantly higher for soils with a lower Pb extractability when treated with EDTA alone. We found no correlation between soil organic matter content and the percentage of the Pb fraction bound to soil organic matter (where from 25.6+/-1.3% to 73.2+/-0.6% of Pb reside in tested soils) and Pb extractability with EDTA after soil ozonation.     

Effect of metals on the adsorption and extractability of 14C-phenanthrene in soils

The fate of polycyclic aromatic hydrocarbons (PAHs) in contaminated soils may be affected by several environmental factors including the presence of co-contaminants. This study was conducted in order to assess the effect of metals on (i) the adsorption of 14C-phenanthrene in soils and (ii) its extractability and ability to form non-extractable residues. The first objective was accomplished using batch adsorption experiments with an uncontaminated agricultural soil spiked with the metals Cd, Cu, Pb, and Zn. Adsorption of phenanthrene was significantly higher after the addition of the metals (Kf = 21.48 vs. 8.55) and the desorption less readily reversible when compared to the unspiked soil. The extractability of phenanthrene was assessed with incubation (4 months, laboratory conditions) and microlysimeter experiments (6 months, natural climatic conditions) on three soils spiked with metals. All the soils were labelled with 14C-phenanthrene. The amount of extractable phenanthrene residues was significantly higher when the metals had been added to the soils. Nevertheless, the quantity of non-extractable residues was non-significantly different between the spiked and unspiked soils. The mechanism leading to increased adsorption and extractability of phenanthrene in the presence of metals is still unknown. In perspective, it would be interesting to assess the bioavailability of PAHs in the presence of metals in further experiments.     

Laboratory studies on volatilization and mineralization of 14c‐p,p'‐DDT in soil,release of bound residues and dissipation from solid surfaces

Abstract

In support of field data, laboratory studies were conducted on volatilization, mineralization and binding of ¹⁴C‐p,p'‐DDT in soils at Sao Paulo. Incubation of soil for 6 weeks did not result in volatilized organics or mineralization; with >95% extractable radiocarbon in the form of p,p'‐DDT. Small amounts of bound residues (1.8%) were detected in soil. These data confirm the very slow dissipation of DDT in the field which presumably relates to the acidic pH of soil (4.5–4.8).

Bound ¹⁴C‐residues in soils treated with ¹⁴C‐p,p'‐DDT at Praia Grande and Sao Paulo could be released (5–21%) by sulphuric acid treatment. The released residue had the composition: 69–90% DDT, 7–32% DDD and 0–3% DDE. Incubation of soil bound ¹⁴C‐residues with fresh inoculum for 3 months did not result in release of ¹⁴C.

Dissipation from wooden surfaces was fairly slow. After 20 weeks, 74% of the applied radioactivity could be recovered; 44% hexane‐non‐extractable.     

Growth response and phytoextraction of copper at different levels in soils by Elsholtzia splendens

Phytoremediation is a promising approach for cleaning up soils contaminated with heavy metals. Information is needed to understand growth response and uptake mechanisms of heavy metals by some plant species with exceptional capability in absorbing and superaccumulating metals from soils. Greenhouse study, field trial, and old mined area survey were conducted to evaluate growth response and Cu phytoextraction of Elsholtzia splendens in contaminated soils, which has been recently identified to be tolerant to high Cu concentration and have great potential in remediating contaminated soils. The results from this study indicate that the plant exhibited high tolerance to Cu toxicity in the soils, and normal growth was attained up to 80 mg kg(-1) available soil Cu (the NH4OAc extractable Cu) or 1000 mg kg(-1) total Cu. Under the field conditions, a biomass yield of 9 ton ha(-1) was recorded at the soil available Cu level of 77 mg kg(-1), as estimated by the NH4OAc extraction method. Concentration-dependent uptake of Cu by the plant occurred mainly at the early growth stage, and at the late stage, there is no difference in shoot Cu concentrations grown at different extractable soil Cu levels. The extractability of Cu from the highly polluted soil is much greater by the roots than that by the shoots. The NH4OAc extractable Cu level in the polluted soil was reduced from 78 to 55 mg kg(-1) in the soil after phytoextraction and removal of Cu by the plant species for one growth season. The depletion of extractable Cu level in the rhizosphere was noted grown in the mined area, even at high Cu levels, the NH4OAc extractable Cu in the rhizosphere was 30% lower than that in the bulk soil. These results indicate that phytoextraction of E. splendens can effectively reduce the plant-available Cu level in the polluted soils.     

Bioaccumulation and human health risk assessment of chromium and nickel in paddy rice grown in serpentine soils

The natural abundance of Cr and Ni in serpentine soils is well-known, but the food safety of rice grown in these hazardous paddy soils is poorly understood. The study evaluated the bioaccumulation of chromium (Cr) and nickel (Ni) in rice (Oryza sativa) grown in serpentine-derived paddy soils in the Philippines. Surface soil (0–20 cm) samples were collected and characterized across three (i.e., Masinloc, Candelaria, and Sta. Cruz) paddy areas in Luzon Island, Philippines. At least 3 to 4 whole rice plants at mature stage were uprooted manually in each sampling point where the soil samples were collected. The total Cr and Ni concentrations in rice (i.e., roots, shoots, and grains) and soil, soil physicochemical properties, bioaccumulation factor (BAF), translocation factor (TF), and the hazard quotients (HQ) were determined. Results revealed that Cr and Ni in rice were accumulated mostly in the roots. Although paddy soils had elevated total Cr and Ni concentrations, the BAF and soil-to-root TF values for Cr and Ni were < 1. In terms of human health risks, results further revealed low risk for both male and female Filipino adults as HQ values for Cr and Ni were < 1. While it is safe to consume rice grown in the area in terms of Cr and Ni dietary intake, more studies are necessary to understand the dynamics and bioavailability of these heavy metals in other crops and drinking water from tube wells in these areas in order to provide a more holistic human health-based assessments and to ensure consumer safety in serpentine areas. In addition, a more reliable data on Cr and Ni speciation in serpentine soils and crops is critically important. Further studies are also needed to understand the contribution of bioavailable heavy metals in improving the soil health to achieve food safety.

     

Copper contamination in paddy soils irrigated with wastewater

Copper (Cu) contamination was investigated in paddy soils where Cu-rich wastewater (12 mg Cu/l) was used for irrigation. The results showed that Cu contamination increased the soil Cu content from 17.0 mg Cu/kg in the non-wastewater irrigated soils (NWIS) to 101.2 mg Cu/kg in the wastewater irrigated soils (WIS), and Cu accumulated mostly in the surface layer (0-10 cm) of the paddy soil. The average Cu contents in brown rice, rice hull and rice straw from NWIS were 1.4, 7.3 and 14.5 mg Cu/kg, while those from WIS were 15.5, 133.2, and 101.4 mg Cu/kg, respectively. Correlation analysis revealed that the relationship between the Cu content in the rice straw and the rice hull with the total Cu content of the soil could be described by an exponential function (R2 = 0.921 and 0.831, respectively; P <0.01). Rice plants grown in the WIS showed symptoms of black roots, less effective tiller, etc. Subsequently, the rice yield decreased by 18-25%, compared with that grown in NWIS.     

Adsorption, desorption, and mobility of permethrin in Malaysian soils

The adsorption, desorption, and mobility of permethrin in six tropical soils was determined under laboratory and greenhouse conditions. The six soils were selected from vegetable growing areas in Malaysia. Soil organic matter (OM) was positively correlated (r2 = 0.97) with the adsorption of permethrin. The two soils, namely, Teringkap 1 and Lating series with the highest OM (3.2 and 2.9%) released 32.5 and 30.8% of the adsorbed permethrin after four consecutive repetitions of the desorption process, respectively, compared to approximately 75.4% of the Gunung Berinchang soil with the lowest OM (1.0%) under the same conditions. The mobility of permethrin down the soil column was inversely correlated to the organic matter content of the soil. Permethrin residue penetrated only to the 10-15 cm zone in the Teringkap 1 soil with 3.2% OM but penetrated to a depth of more than 20 cm in the other soils. The Berinchang series soil with the lowest OM (1.0%) yielded leachate with 14.8% permethrin, the highest level in leachates from all the soils tested. Therefore, the possibility for permethrin to contaminate underground water may be greater in the presence of low organic matter content, which subsequently allows a higher percentage of permethrin to move downwards through the soil column.     

Remediation mechanisms of mercapto-grafted palygorskite for cadmium pollutant in paddy soil

The immobilization agent was the key factor that determined the success of remediation of heavy metal polluted soil. In this study, mercapto-grafted palygorskite (MP) as a novel and efficient immobilization agent was utilized for the remediation of Cd-polluted paddy soil in pot trials, and the remediation mechanisms were investigated in the aspect of soil chemistry and plant physiology with different rice cultivars as model plants. Mercapto-grafted palygorskite at applied doses of 0.1–0.3% could reduce Cd contents of brown rice and straws of different cultivars significantly. Both reduced DTPA-extractable Cd contents in rhizosphere and non-rhizosphere soil and decreasing Cd contents in iron plaques on rice root surfaces confirmed that MP was an efficient immobilization agent for Cd pollutant in paddy soil. In the aspect of soil chemistry, the pH values of rhizosphere and non-rhizosphere soils had no statistical changes in the MP treatment groups, but their zeta potentials decreased obviously, indicating that MP could enhance the fixation or sorption of Cd on soil compositions. In the aspect of antioxidant system, MP could increase POD activity of rice roots significantly to alleviate the stress of Cd to roots, and resulted in the decrease of T-AOC, SOD, and CAT activities of rice roots of the selected cultivars. MP had no inhabitation or enhancement effects on TSH of rice roots but enhance the contents of MTs and NPT to binding Cd to complete detoxification process. MP as a novel and efficient immobilization agent could complete the remediation effects through soil chemistry and plant physiological mechanisms.

     

Partitioning of arsenic in soil-crop systems irrigated using groundwater: a case study of rice paddy soils in southwestern Taiwan

The accumulation of As in rice due to groundwater irrigation in paddy fields represents a serious health hazard in South and Southeast Asia. In Taiwan, the fate of As in long-term irrigated paddy fields is poorly understood. Groundwater, surface soil, and rice samples were collected from a paddy field that was irrigated with As-containing groundwater in southwestern Taiwan. The purpose of this study is to elucidate the source and sink of As in the paddy field by comparing the As fractions in the soils that were obtained by a sequential extraction procedure (SEP) with the As uptake of rice. The risks associated with eating rice from the field can thus be better understood. The concentration of As in groundwater varied with time throughout the growing seasons of rice, but always exceeded the permitted maximum (10 μg L⁻¹) for drinking water by the WHO. The As concentration increased with the concentration of Fe in the groundwater, supporting the claim that a large amount of As was concentrated in the Fe flocs collected from the internal wall of the groundwater pump. The results of the SEP revealed that As bound with amorphous and crystalline hydrous oxides exhibited high availability in the soils. The root of rice accumulated the largest amount of As, followed by the straw, husk, and grain. Although the As concentration in the rice grain was less than 1.0 mg kg⁻¹, the estimated intake level was close to the maximum tolerable daily intake of As, as specified by the WHO.     

Simulation of global warming potential (GWP) from rice fields in the Tai-Lake region,China by coupling 1:50,000 soil database with DNDC model

Quantifying greenhouse gas (GHG) emissions from wetland ecosystems is a relatively new issue in global climate change studies. China has approximately 22% of the world's rice paddies and 38% of the world's rice production, which are crucial to accurately estimate the global warming potential (GWP) at regional scale. This paper reports an application of a biogeochemical model (DeNitrification and DeComposition or DNDC) for quantifying GWP from rice fields in the Tai-Lake region of China. For this application, DNDC is linked to a 1:50,000 soil database, which was derived from 1107 paddy soil profiles compiled during the Second National Soil Survey of China in the 1980–1990s. The simulated results show that the 2.34 Mha of paddy soil cultivated in rice–wheat rotation in the Tai-Lake region emitted about ?1.48 Tg C, 0.84 Tg N and 5.67 Tg C as CO₂, N₂O, and CH₄ respectively, with a cumulative GWP of 565 Tg CO₂ equivalent from 1982 to 2000. As for soil subgroups, the highest GWP (26,900 kg CO₂ equivalent ha^?1 yr^?1) was linked to gleyed paddy soils accounting for about 4.4% of the total area of paddy soils. The lowest GWP (5370 kg CO₂ equivalent ha^?1 yr^?1) was associated with submergenic paddy soils accounting for about 0.32% of the total area of paddy soils. The most common soil in the area was hydromorphic paddy soils, which accounted for about 53% of the total area of paddy soils with a GWP of 12,300 kg CO₂ equivalent ha^?1 yr^?1. On a regional basis, the annual averaged GWP in the polder, Tai-Lake plain, and alluvial plain soil regions was distinctly higher than that in the low mountainous and Hilly soil regions. As for administrative areas, the average annual GWP of counties in Shanghai city was high. Conversely, the average annual GWP of counties in Jiangsu province was low. The high variability in soil properties throughout the Tai-Lake region is important and affects the net greenhouse gas emissions. Therefore, the use of detailed soil data sets with high-resolution digital soil maps is essential to improve the accuracy of GWP estimates with process-based models at regional and national scales.     

Level and distribution of DDT in surface soils from Tianjin, China

One hundred and eighty eight surface soil samples were collected from the Tianjin area to study the contamination of DDT and its metabolites. Measurements were taken for p,p'-DDE, p,p'-DDD, p,p'-DDT, o,p'-DDE, o,p'-DDD and o,p'-DDT for all samples. The results indicated that p,p'-DDT and p,p'-DDE were the predominant contaminant compounds in the surface soil samples, with mean concentrations of 27.5 and 18.8 ng g(-1) respectively. No significant differences in DDT concentrations were found between the soils from wastewater treated irrigated areas and other areas, suggesting that wastewater irrigation is not an important source of DDT in the area. However, the spatial distribution of soil DDTs levels in the area did correlate well with early direct application rates of pesticides. In addition, both pH level and organic carbon content are also known factors affecting the level of DDT and its metabolites. Although it was assumed that the use of these chemicals was banned in the early 1980s, the current concentration levels appear to be too high to be mere residuals after 20 years degradation.     

Differential bioavailability of field-weathered p,p'-DDE to plants of the Cucurbita and Cucumis genera

Field experiments were conducted to assess the bioavailability of weathered p,p'-DDE in soil to plants in the Cucurbita (squash, pumpkin) and Cucumis (cucumber, melon) genera. As expected, significant variability exists in the uptake of p,p'-DDE between plants of different genera. Root:soil concentration factors, defined as the ratio of p,p'-DDE (ng/g, dry weight) in the roots to that in the soil, approach 1.8 for cucumbers/melons and 16 for squash/pumpkin. However, significant differences were also observed among varieties of squash and pumpkin, with greater than an order of magnitude variation in the root:soil concentration factors and up to two orders of magnitude difference in the absolute amount of contaminant present within the plant. Although root systems routinely contain the highest concentration of p,p'-DDE (ng/g), this compartment comprises less than 2% of the total plant biomass. In all varieties but one, more than 86% of the extracted pollutant was in the shoot system. For two of varieties of Cucurbita pepo, concentrations of p,p'-DDE in the stems reached 1.1-2.2 mg/g and estimations of percent contaminant extraction from the soil ranged from 0.40% to 2.4%. These values approach those observed in the phytoremediation of heavy metals by "hyperaccumulating" species and indicate the potential for a plant-based remediation approach to soils contaminated with persistent organic pollutants.     

Adsorption,Desorption, and Mobility of Permethrin in Malaysian Soils

Abstract

The adsorption, desorption, and mobility of permethrin in six tropical soils was determined under laboratory and greenhouse conditions. The six soils were selected from vegetable growing areas in Malaysia. Soil organic matter (OM) was positively correlated (r ² = 0.97) with the adsorption of permethrin. The two soils, namely, Teringkap 1 and Lating series with the highest OM (3.2 and 2.9%) released 32.5 and 30.8% of the adsorbed permethrin after four consecutive repetitions of the desorption process, respectively, compared to approximately 75.4% of the Gunung Berinchang soil with the lowest OM (1.0%) under the same conditions. The mobility of permethrin down the soil column was inversely correlated to the organic matter content of the soil. Permethrin residue penetrated only to the 10–15 cm zone in the Teringkap 1 soil with 3.2% OM but penetrated to a depth of more than 20 cm in the other soils. The Berinchang series soil with the lowest OM (1.0%) yielded leachate with 14.8% permethrin, the highest level in leachates from all the soils tested. Therefore, the possibility for permethrin to contaminate underground water may be greater in the presence of low organic matter content, which subsequently allows a higher percentage of permethrin to move downwards through the soil column.