Distribution of polychlorinated biphenyls and chlorinated pesticide residues in trout in the Sierra Nevada

Organochlorine compounds are known to be atmospherically transported to long distances from their original sources. To understand the influence of California's Sierra Nevada range on the air transport and subsequent distribution pattern of some of these residues within the range, we have chosen salmonid fish as an indicator species. Fish were collected from 10 locations throughout the northern and central Sierra Nevada and polychlorinated biphenyl (PCB), toxaphene, chlordane, and DDT [1,1,1-trichloro, 2,2'-bis (p-chlorophenyl) ethane] residues in muscle tissue were analyzed. Rainbow trout (Oncorhynchus mykiss) were found in all sampling locations, and therefore analyses mainly focused on this species. When similar-sized rainbow trout samples from several similar oligotrophic, high-altitude lakes and streams were compared, it became apparent that altitude is one of the factors affecting the residual levels of PCB (r(2) = 0.882), but not for total DDT, toxaphene, or chlordane in trout. Analysis of correlations among these four organochlorine compound residue groups indicated that there are modest correlations in patterns of distribution between chlordane vs. toxaphene (r(2) = 0.345), and chlordane vs. total DDT (r(2) = 0.239), but toxaphene residues are not correlated with PCB or total DDT. In view of significant correlation to the altitude it is concluded that PCB residue in rainbow trout is a good monitoring tool for studying the effect of high-altitude mountain ranges on the long-range transport and distribution of those persistent pollutants.     

Distribution of polychlorinated biphenyls in the Fort Edward,New York,water system

Levels of polychlorinated biphenyls (PCBs) have been determined in the water, in the soils and sediments, and in the biota of a small upstate New York public water supply system, which is near the heavily polluted section of the Hudson River and a disposal site for PCB-containing waste. The impounded water exhibits a significant and relatively uniform level of Aroclor 1016, whereas the ground and surface waters supplying the reservoir do not. Rainfall, which exhibits a high level of Aroclor 1016, constitutes a small but significant source of PCB input. Soil and sediment samples exhibit significant median levels of both Aroclor 1016 and Aroclor 1254, but the local concentrations vary widely. The biota exhibit much higher PCB levels than the water or sediments, and show a strong preference for Aroclor 1254. The PCB levels in the macroinvertebrates are particularly high, suggesting that these organisms may provide a useful indicator for monitoring PCB contamination in aquatic systems. Risk assessment indicates that the lifetime incremental risk of cancer associated with the drinking water is below 10^–6. Management of such low levels of PCB contamination is best achieved by reducing the input of PCBs.     

Simulating long-term and residual effects of nitrogen fertilization on corn yields, soil carbon sequestration, and soil nitrogen dynamics

Soil carbon sequestration (SCS) has the potential to attenuate increasing atmospheric CO2 and mitigate greenhouse warming. Understanding of this potential can be assisted by the use of simulation models. We evaluated the ability of the EPIC model to simulate corn (Zea mays L.) yields and soil organic carbon (SOC) at Arlington, WI, during 1958-1991. Corn was grown continuously on a Typic Argiudoll with three N levels: LTN1 (control), LTN2 (medium), and LTN3 (high). The LTN2 N rate started at 56 kg ha(-1) (1958), increased to 92 kg ha(-1) (1963), and reached 140 kg ha(-1) (1973). The LTN3 N rate was maintained at twice the LTN2 level. In 1984, each plot was divided into four subplots receiving N at 0, 84, 168, and 252 kg ha(-1). Five treatments were used for model evaluation. Percent errors of mean yield predictions during 1958-1983 decreased as N rate increased (LTN1 = -5.0%, LTN2 = 3.5%, and LTN3 = 1.0%). Percent errors of mean yield predictions during 1985-1991 were larger than during the first period. Simulated and observed mean yields during 1958-1991 were highly correlated (R2 = 0.961, p < 0.01). Simulated SOC agreed well with observed values with percent errors from -5.8 to 0.5% in 1984 and from -5.1 to 0.7% in 1990. EPIC captured the dynamics of SOC, SCS, and microbial biomass. Simulated net N mineralization rates were lower than those from laboratory incubations. Improvements in EPIC's ability to predict annual variability of crop yields may lead to improved estimates of SCS.     

Aging effects on cadmium transport in undisturbed contaminated sandy soil columns

Limited information is available on the effects of contaminant aging (i.e., the contact time of Cd with the soil) on Cd transport in soils. We conducted displacement experiments in which indigenous Cd and freshly applied Cd were leached simultaneously from undisturbed samples of three Spodosol horizons. Sorption of Cd was described using Freundlich isotherms, whereas transport was described as a convection-dispersion process. Parameter optimization analysis using a mobile-immobile transport model applied to nonsorbing tracer displacement data showed that 16 to 22% of the water in the columns was immobile. The low dimensionless mass transfer coefficients in the mobile-immobile model were indicative of diffusion-limited transfer between mobile and immobile water, and hence physical nonequilibrium. A two-site kinetic sorption model could be fitted closely to breakthrough curves of the non-aged Cd for three soil horizons. No conclusive evidence was found that contaminant aging in soil affects cadmium transport. On the one hand, predictions of aged Cd leaching, using parameters estimated from displacement experiments with nonaged Cd, differed from those for the aged Cd in the E horizon. On the other hand, no meaningful differences in transport behavior between aged and non-aged Cd were found for the humus Bh and Bh/C horizons. The two-site kinetic rate coefficient alphac was found to depend on water flux, further indicating that mass transfer between sorption sites and the liquid is limited by diffusion rather than by kinetic sorption.     

Immobilization of cesium-137 and uranium in contaminated sediments using soil amendments

Batch and dynamic leaching methods were used to evaluate the effectiveness of hydroxyapatite (HA), illite, and zeolite, alone and in combination, as soil additives for reducing the migration of cesium-137 (137Cs+) and uranium (U) from contaminated sediments. Amendment treatments ranging from 0 to 50 g kg(-1) were added to the sediment and equilibrated in 0.001 M CaCl2. After equilibration, the treatment supernatants were analyzed for 137Cs+, U, PO4, and other metals. The residual sediments were then extracted overnight using one of the following: 1.0 M NH4Cl, 0.5 M CaCl2, or the Toxicity Characteristic Leaching Procedure (TCLP) extractant. Cesium was strongly sorbed to the contaminated sediments, presumably due to interlayer fixation within native illitic clays. In fact, 137Cs+ was below detection limits in the initial equilibration solutions, the CaCl2 extract, and the TCLP solution, regardless of amendment. Extractants selective for interlayer cations (1.0 M NH4Cl) were necessary to extract measurable levels of 137Cs+. Addition of illitic clays further reduced Cs+ extractability, even when subjected to the aggressive extractants. Zeolite, however, was ineffective in reducing Cs+ mobility when subjected to the aggressive extractants. Hydroxyapatite was less effective than illite at reducing NH4+-extractable Cs+. Hydroxyapatite, and mixtures of HA with illite or zeolite, were highly effective in reducing U extractability in both batch and leaching tests. Uranium immobilization by HA was rapid with similar final U concentrations observed for equilibration times ranging from 1 h to 30 d. The current results demonstrate the effectiveness of soil amendments in reducing the mobility of U and Cs+, which makes in-place immobilization an effective remediation alternative.     

A biotest for evaluating copper bioavailability to plants in a contaminated soil

This work aimed at defining the optimal conditions for a novel ecotoxicological test designed for evaluating the bioavailability and phytotoxicity of metals to plants. This biotest, which provided easy access to roots, shoots, and rhizosphere soil, was applied to a vineyard calcareous soil that had been contaminated by the application of Cu fungicides. A preliminary hydroponic experiment comparing various levels of solution Cu concentration enabled us to determine the no observable adverse effects concentration (NOAEC), which was in the range 5 to 20 microM total Cu (0.01-0.06 microM free Cu ion) for rape (Brassica napus L. cv. Goeland). For the biotest, rape was grown in hydroponic conditions for 21 d in pots designed so that plants developed a planar mat of roots at the surface of a polyamide mesh. By then, the plants were transferred for 4 or 8 d onto a 1- or 3-mm-thick soil layer that was separated from the root mat by the mesh and connected to a reservoir of nutrient solution or deionized water via a filter paper wick. An 8-d period was the best option as it enabled plant growth to be significant. The use of 1-mm soil thickness was recommended if the biotest aimed at investigating root-induced changes in the rhizosphere. Although it may cause some artifacts, compared with deionized water, nutrient solution provided better standardized conditions for comparing widely differing soil samples. The studied soil did not induce any Cu phytotoxicity in spite of its fairly large total Cu content.     

Recycling contaminated soil as alternative raw material in cement facilities: Life cycle assessment

Volcanic soil can be used to remove metals from wastewaters. Once used, it is disposed in landfills. The utilization of this material in the cement industry as an alternative raw material was evaluated using life cycle assessment (LCA) methodology. This possibility has been studied from an environmental point of view in a Chilean cement facility, representative of the current operation state of art, including both technical and economic analysis. Two scenarios were compared: Scenario 1, which corresponds to the existing cement production process, and Scenario 2, which represents cement production using spent volcanic soil. With the exception of the categories of carcinogens (C) and minerals (M), the comparative results are favourable to Scenario 2, specially regarding to the category of ecotoxicity (E), mainly due to the avoided landfilling emissions of the volcanic soil. When considering the damage assessment, damage to human health (HH), ecosystem quality (EQ) and resources (R) are lower in Scenario 2. In addition, sensitivity analyses were performed to study the influence of particular parameters (i.e., transport of spent volcanic soil, CO₂ emissions from the clinkerization process and heavy metals leaching from the spent volcanic soil) on the results of the assessment. The use of alternative raw materials (in this case, spent volcanic soil), which present the advantage to be wastes from other technical systems, appear to allow the development of cement production in a more sustainable way, slightly improving the economy of the process. The spent volcanic soil can be treated with zero cost for the wastewater treatment plant with savings of 0.23€ for each tonne of clinker production. Establishing a sound management way for the spent volcanic soil could foment its possible use as mineral adsorbent in industrial wastewater treatment facilities.     

In situ speciation studies of copper-humic substances in a contaminated soil during electrokinetic remediation

Speciation of copper-humic substances (HS) in the electrokinetic remediation (EKR) of a contaminated soil was studied by in situ extended X-ray absorption fine structure (EXAFS) and X-ray absorption near edge structure (XANES) spectroscopies. The least-square fits of the XANES spectra suggested that the main Cu species in the contaminated soil were Cu-HS (50%), CuCO(3) (28%), Cu(2)O (11%), and CuO (11%). The Cu-HS in the contaminated soil possessed equatorial and axial Cu-O bond distances of 1.94 and 2.17 A with coordination numbers (CNs) of 3.6 and 1.4, respectively. In the EKR process, the axial Cu-O bond distance in the Cu-HS complexes was increased by 0.15 A, which might be due to a ligand exchange of the Cu-HS with H(2)O molecules in the electrolyte. After 180 min of EKR, about 50% of the Cu-HS complexes (or 24% of total Cu) in the soil were dissolved and formed [Cu(H(2)O)(6)](2+) in the electrolyte, 71% (or 17% of total Cu in the soil) of which were migrated to the cathode under the electric field (5 V/cm). This work exemplifies the use of in situ EXAFS and XANES spectroscopies for speciation studies of Cu chelated with HS in the contaminated soil during EKR.     

Regional patterns of soil organic carbon stocks in China

Soil organic carbon (SOC) is of great importance in the global carbon cycle. Distribution patterns of SOC in various regions of China constitute a nation-wide baseline for studies on soil carbon changes. This paper presents an integrated and multi-level study on SOC stock patterns of China, and presents baseline SOC stock estimates by great administrative regions, river watersheds, soil type regions and ecosystem. The assignment is done by means of a recently completed 1: 1,000,000 scale soil database of China, which is the most detailed and reliable one in China at the present time. SOC densities of 7292 soil profiles collected across China in the middle of the 1980s were calculated and then linked to corresponding polygons in a digital soil map, resulting in a SOC Density Map of China on a 1: 1,000,000 scale, and a 1 km x 1 km grid map. Corresponding maps of administrative regions, river watersheds, soil types (ST), and ecosystems in China were also prepared with an identical resolution and coordinate control points, allowing GIS analyses. Results show that soils in China cover an area of 9.281 x 10(6)km(2) in total, with a total SOC stock of 89.14 Pg (1 Pg=10(15)g) and a mean SOC density of 96.0 t C/ha. Confidence limits of the SOC stock and density in China are estimated as [89.23 Pg, 89.08 Pg] and [96.143 t C/ha, 95.981 t C/ha] at 95% probability, respectively. The largest total SOC stock (23.60 Pg) is found in South-west China while the highest mean SOC density (181.9 t C/ha) is found in north-east China. The total SOC stock and the mean SOC density in the Yangtze river watershed are 21.05 Pg and 120.0 t C/ha, respectively, while the corresponding figures in the Yellow river watershed are 8.46 Pg and 104.3 t C/ha, respectively. The highest total SOC stocks are found in Inceptisols (34.39 Pg) with SOC density of 102.8 t C/ha. The lowest and highest mean SOC densities are found on Entisols (28.1 t C/ha), and on Histosols (994.728.1 t C/ha), respectively. Finally, the total SOC stock in shrub and forest ecosystem classes are 25.55 and 21.50 Pg, respectively; the highest mean SOC density (209.9 t C/ha) was recorded in the wetland ecosystem class and the lowest (29.0 t C/ha) in the desert ecosystem class. Among five forest ecosystem types, Evergreen conifer forest stores the highest SOC stock (6.81 Pg), and Deciduous conifer forest shows the highest SOC density (225.9 t C/ha). Figures of SOC stocks stratified by Administrative regions, river watersheds, soil types and ecosystem types presented in the study may constitute national-wide baseline for studies of SOC stock changes in various regions in the future.     

Degradation of polycyclic aromatic hydrocarbons by combined chemical pre-oxidation and bioremediation in creosote contaminated soil

The ability of pre-oxidation to overcome polycyclic aromatic hydrocarbons (PAH) recalcitrance to biodegradation was investigated in creosote contaminated soil. Sand and peat artificially spiked with creosote (quality WEI C) were used as model systems. Ozonation and Fenton-like treatment were proved to be feasible technologies for PAH degradation in soil. The efficiency of ozonation was strongly dependent on the water content of treated soil samples. The removal of PAH by Fenton-like treatment depended on the applied H2O2/soil weight ratio and ferrous ions addition. It was determined that the application of chemical oxidation in sand resulted in a higher PAH removal and required lower oxidant (ozone, hydrogen peroxide) doses. The enhancement of PAH biodegradability by different pre-treatment technologies also depended on the soil matrix. It was ascertained that combined chemical and biological treatment was more efficient in PAH elimination in creosote contaminated soil than either one alone. Thus, the combination of Fenton-like and the subsequent biological treatment resulted in the highest removal of PAH in creosote contaminated sand, and biodegradation with pre-ozonation was found to be the most effective technology for PAH elimination in peat.     

Tillage and crop residue effects on soil carbon and carbon dioxide emission in corn-soybean rotations

Soil C change and CO2 emission due to different tillage systems need to be evaluated to encourage the adoption of conservation practices to sustain soil productivity and protect the environment. We hypothesize that soil C storage and CO2 emission respond to conservation tillage differently from conventional tillage because of their differential effects on soil properties. This study was conducted from 1998 through 2001 to evaluate tillage effects on soil C storage and CO2 emission in Clarion-Nicollet-Webster soil association in a corn [Zea mays L.]-soybean [Glycine max (L.) Merr.] rotation in Iowa. Treatments included no-tillage with and without residue, strip-tillage, deep rip, chisel plow, and moldboard plow. No-tillage with residue and strip-tillage significantly increased total soil organic C (TC) and mineral fraction C (MFC) at the 0- to 5- and 5- to 10-cm soil depths compared with chisel plow after 3 yr of tillage practices. Soil CO2 emission was lower for less intensive tillage treatments compared with moldboard plow, with the greatest differences occurring immediately after tillage operations. Cumulative soil CO2 emission was 19 to 41% lower for less intensive tillage treatments than moldboard plow, and it was 24% less for no-tillage with residue than without residue during the 480-h measurement period. Estimated soil mineralizable C pool was reduced by 22 to 66% with less intensive tillage treatments compared with moldboard plow. Adopting less intensive tillage systems such as no-tillage, strip-tillage, deep rip, and chisel plow and better crop residue cover are effective in reducing CO2 emission and thus improving soil C sequestration in a corn-soybean rotation.     

In situ reduction of chromium(VI) in heavily contaminated soils through organic carbon amendment

Chromium has become an important soil contaminant at many sites, and facilitating in situ reduction of toxic Cr(VI) to nontoxic Cr(III) is becoming an attractive remediation strategy. Acceleration of Cr(VI) reduction in soils by addition of organic carbon was tested in columns pretreated with solutions containing 1000 and 10 000 mg L(-1) Cr(VI) to evaluate potential in situ remediation of highly contaminated soils. Solutions containing 0,800, or 4000 mg L(-1) organic carbon in the form of tryptic soy broth or lactate were diffused into the Cr(VI)-contaminated soils. Changes in Cr oxidation state were monitored through periodic micro-XANES analyses of soil columns. Effective first-order reduction rate constants ranged from 1.4 x 10(-8) to 1.5 x 10(-7) s(-1), with higher values obtained for lower levels of initial Cr(VI) and higher levels of organic carbon. Comparisons with sterile soils showed that microbially dependent processes were largely responsible for Cr(VI) reduction, except in the soils initially exposed to 10 000 mg L(-1) Cr(VI) solutions that receive little (800 mg L(-1)) or no organic carbon. However, the microbial populations (< or = 2.1 x 10(5) g(-1)) in the viable soils are probably too low for direct enzymatic Cr(VI) reduction to be important. Thus, synergistic effects sustained in whole soil systems may have accounted for most of the observed reduction. These results show that acceleration of in situ Cr(VI) reduction with addition of organic carbon is possible in even heavily contaminated soils and suggest that microbially dependent reduction pathways can be dominant.     

Modeling organic carbon dynamics and cadmium fate in long-term sludge-amended soil

A model is described that may help to resolve uncertainty and controversy over the long-term consequences of sludge applications to arable land, especially with regard to the effects of sludge adsorption characteristics on trace metal solubility and bioavailability (e.g., the sludge "time bomb" or sludge "protection" hypotheses). Mass balances of organic and inorganic material derived from sludge and crop residues are simulated. Each pool has a potentially different adsorption affinity for trace metals, and this leads to changes in the adsorption capacity of sludge-amended soil that influence leaching and crop uptake. Model simulations were compared with measured changes in organic carbon and ethylenediaminetetraacetic acid (EDTA)-extractable cadmium contents in a clay loam soil following 41 years of sludge applications. The model adequately reproduced the data, although discrepancies in the vertical distribution of Cd were attributed to the effects of macropore transport and root-uptake driven recirculation. A Monte Carlo sensitivity analysis demonstrated that the most important parameters affecting leaching and crop uptake were the Cd loading and parameters controlling adsorption, especially the partition coefficient for sludge-derived inorganic material and the exponent regulating the effect of pH on sorption. Scenario simulations show that no general conclusions can be drawn with respect to the validity of the sludge "time bomb" and sludge "protection" hypotheses. Either may occur, or neither, depending on three key system parameters: the ratio of sludge adsorption capacity to the initial adsorption capacity of the soil, the proportion of the sludge adsorption capacity contributed by the inorganic fraction, and the sludge Cd loading.     

EPIC modeling of soil organic carbon sequestration in croplands of Iowa

Depending on management, soil organic carbon (SOC) is a potential source or sink for atmospheric CO(2). We used the EPIC model to study impacts of soil and crop management on SOC in corn (Zea mays L.) and soybean (Glycine max L. Merr.) croplands of Iowa. The National Agricultural Statistics Service crops classification maps were used to identify corn-soybean areas. Soil properties were obtained from a combination of SSURGO and STATSGO databases. Daily weather variables were obtained from first order meteorological stations in Iowa and neighboring states. Data on crop management, fertilizer application and tillage were obtained from publicly available databases maintained by the NRCS, USDA-Economic Research Service (ERS), and Conservation Technology Information Center. The EPIC model accurately simulated state averages of crop yields during 1970-2005 (R(2) = 0.87). Simulated SOC explained 75% of the variation in measured SOC. With current trends in conservation tillage adoption, total stock of SOC (0-20 cm) is predicted to reach 506 Tg by 2019, representing an increase of 28 Tg with respect to 1980. In contrast, when the whole soil profile was considered, EPIC estimated a decrease of SOC stocks with time, from 1835 Tg in 1980 to 1771 Tg in 2019. Hence, soil depth considered for calculations is an important factor that needs further investigation. Soil organic C sequestration rates (0-20 cm) were estimated at 0.50 to 0.63 Mg ha(-1) yr(-1) depending on climate and soil conditions. Overall, combining land use maps with EPIC proved valid for predicting impacts of management practices on SOC. However, more data on spatial and temporal variation in SOC are needed to improve model calibration and validation.     

Denitrification and availability of carbon and nitrogen in a well-drained pasture soil amended with particulate organic carbon

A well-drained soil in N-fertilized dairy pasture was amended with particulate organic carbon (POC), either sawdust or coarse woody mulch, and sampled every 4 wk for a year to test the hypothesis that the addition of POC would increase denitrification activity by increasing the number of microsites where denitrification occurred. Overall mean denitrifying enzyme activity (DEA), on a gravimetric basis, was 100% greater for the woody mulch treatment and 50% greater for the sawdust treatment compared with controls, indicating the denitrifying potential of the soil was enhanced. Despite differences in DEA, no difference in denitrification rate, as measured by the acetylene block technique, was detected among treatments, with an average annual N loss of ～22 kg N ha yr Soil water content overall was driving denitrification in this well-drained soil as regression of the natural log of volumetric soil water content (VWC) against denitrification rate was highly significant ( = 0.74, < 0.001). Addition of the amendments, however, had significant effects on the availability of both C and N. An additional 20 to 40 kg N ha was stored in POC-amended treatments as a result of increases in the microbial biomass. Basal respiration, as a measure of available C, was 400% greater than controls in the sawdust treatment and 250% greater than controls in the mulch. Net N mineralization, however, was significantly lower in the sawdust treatment, resulting in significantly lower nitrate N levels than in the control. We attribute the lack of measured response in denitrification rate to the high temporal variability in denitrification and suggest that diffusion of nitrate may ultimately have limited denitrification in the amended treatments. Our data indicate that manipulation of denitrification by addition of POC may be possible, particularly when nitrate levels are high, but quantifying differences in the rate of denitrification is difficult because of the temporal nature of the process (particularly the complex interaction of N availability and soil water content).     

Cadmium and zinc in vegetation and litter of a voluntary woodland that has developed on contaminated sediment-derived soil

Vegetation that develops spontaneously on metal-contaminated soils presents an opportunity to evaluate both metal bioavailability and the risks posed to biota. The behavior of Cd and Zn in the species of a spontaneously developed woodland, colonizing a canal embankment, has been investigated. Nitric-acid-extractable metal concentrations in the sediment-derived substrate ranged between 5.0 to 376 mg kg(-1)dry wt. Cd and 83.0 to 784 mg kg(-1)dry wt. Zn. The woodland is dominated by Willow (Salix) species. Salix caprea selectively accumulated Cd in all stem tissues, in contrast to S. viminalis, which regulated tissue Cd content. Both species showed an effective regulation of tissue Zn. Cadmium uptake by S. caprea was correlated with differences in soil pH, while Zn uptake was not. There was no relationship between tissue metal concentrations and soil metal nitric acid-extractable concentrations. Other aspects of ecosystem function appeared unaffected by the elevated Cd flux in S. caprea; leaf litter organisms present represented all major groups and there was no accumulation of organic matter. The woodland represents a potentially sustainable option for remediating a low value site with difficult access that does not involve removal of the contaminated material to a landfill or making a permanent inert cover.     

Zinc fractionation in contaminated soils by sequential and single extractions: influence of soil properties and zinc content

We studied the fractionation of zinc (Zn) in 49 contaminated soils as influenced by Zn content and soil properties using a seven-step sequential extraction procedure (F1: NH4NO3; F2: NH4-acetate, pH 6; F3: NH3OHCl, pH 6; F4: NH4-EDTA, pH 4.6; F5: NH4-oxalate, pH 3; F6: NH4-oxalate/ascorbic acid, pH 3; F7: residual). The soils had developed from different geologic materials and covered a wide range in soil pH (4.0-7.3), organic C content (9.3-102 g kg(-1)), and clay content (38-451 g kg(-1)). Input of aqueous Zn with runoff water from electricity towers during 26 to 74 yr resulted in total soil Zn contents of 3.8 to 460 mmol kg(-1). In acidic soils (n = 24; pH <6.0), Zn was mainly found in the mobile fraction (F1) and the last two fractions (F6 and F7). In neutral soils (n = 25; pH > or =6.0), most Zn was extracted in the mobilizable fraction (F2) and the intermediate fractions (F4 and F5). The extractability of Zn increased with increasing Zn contamination of the soils. The sum of mobile (F1) and mobilizable (F2) Zn was independent of soil pH, the ratio of Zn in F1 over F1+F2 plotted against soil pH, exhibited the typical shape of a pH sorption edge and markedly increased from pH 6 to pH 5, reflecting the increasing lability of mobilizable Zn with decreasing soil pH. In conclusion, the extractability of Zn from soils contaminated with aqueous Zn after decades of aging under field conditions systematically varied with soil pH and Zn content. The same trends are expected to apply to aqueous Zn released from decomposing Zn-bearing contaminants, such as sewage sludge or smelter slag. The systematic trends in Zn fractionation with varying soil pH and Zn content indicate the paramount effect of these two factors on molecular scale Zn speciation. Further research is required to characterize the link between the fractionation and speciation of Zn and to determine how Zn loading and soil physicochemical properties affect Zn speciation in soils.     

Food safety assessment of planting patterns of four vegetable-type crops grown in soil contaminated by electronic waste activities

A field experiment was conducted to assess the effect of crop and planting pattern on levels of cadmium (Cd), lead (Pb), and copper (Cu) in crops grown in soil contaminated by electronic waste. The crops were maize (Zea mays L. var. Shentian-1), tomato (Solanum lycopersicum L. var. Zhongshu-4), cabbage (Brassica oleracea L. var. Jingfeng-1), and pakchoi (Brassica chinensis (L.) Makino. var. Youdonger-Hangzhou). The planting patterns were crop monoculture, crop co-planted with a legume, and crop co-planted with another crop. Metal concentrations in the edible parts of the crops varied with types of metals and crops. Pb concentration was higher in leafy vegetables (cabbage and pakchoi) than in maize or tomato, Cd concentration was higher in tomato and pakchoi than in maize or cabbage, and Cu concentration was higher in maize and pakchoi than in tomato or cabbage. Metal concentrations in the edible part were also influenced by planting pattern. Relative to monoculture, co-planting and especially co-planting with Japanese clover tended to decrease Pb accumulation and increase Cd accumulation. According to the maximum permissible concentration (MPC) standard of the National Standard Agency in China, only maize (under all planting patterns) could be safely consumed. Because co-planting tended to increase Cd accumulation even in maize, however, the results suggest that maize monoculture is the optimal crop and planting pattern for this kind of contaminated soil.     

Tests of soil organic carbon density modeled by InTEC in China's forest ecosystems

The integrated terrestrial ecosystem C-budget model (InTEC) developed by Chen and co-workers has been used successfully to predict carbon dynamics of forests in Canada. It was tested here for forest soil organic carbon (SOC) density of China's northern temperate zone and southern subtropical zone. The results show that the simulated SOC density is highly correlated and in broad agreement with observations in Liping and in Changbaishan, representing the southern subtropical zone and the northern temperate zone in China, respectively. SOC density ranged from 2.2 to 11.2 kg/m(2) in Liping and from 3.4 to 14.8 kg/m(2) in Changbaishan. The correlation coefficients (r(2)) are 0.63 (N=16) and 0.76 (N=14) between the simulated and measured data in Liping and Changbaishan, respectively. The SOC densities under different vegetation types in Liping decrease in the order of mixed forest, broadleaf forest, Chinese fir, couch grass, and Chinese redpine, and in Changbaishan in the order of mixed forest, silver fir, larch forest, and birch forest.     

Effects of dissolved organic carbon on sorption and mobility of imidacloprid in soil

To evaluate the effects of dissolved organic carbon on sorption and mobility of the insecticide imidacloprid [1-(6-chloro-3-pyridinyl) methyl-N-nitro-2-imidazolidinimine] in soils, adsorption and column experiments were performed by using a typical calcareous soil from southeastern Spain and two different types of dissolved organic carbon, that is, dissolved organic carbon extracts from a commercial peat (DOC-PE) and high-purity tannic acid (DOC-TA). The experiments were carried out from a 0.01 M CaCl2 aqueous medium at 25 degrees C. The results obtained from the sorption experiments show that the presence of both DOC-PE and DOC-TA, over a concentration range of 15 to 100 mg L(-1), produces in all cases a decreasing amount of imidacloprid adsorbed in the soil studied. From the column experiments the retardation coefficients (RC) were calculated for imidacloprid by using either 0.01 M CaCl2 aqueous solution (RC = 2.10), 0.01 M CaCl2 DOC-PE solution (RC = 1.65), or 0.01 M CaCl2 DOC-TA solution (RC = 1.87). The results indicate that mobility of imidacloprid is increased 21.4 and 11.0% in the presence of DOC-PE and DOC-TA solutions, respectively. Dissolved organic carbon reduces imidacloprid sorption by competing with the pesticide molecules for sorption sites on the soil surface, allowing enhanced leaching of imidacloprid and potentially increasing ground water contamination.