Accumulation of persistent organic pollutants in the food chain of lake baikal

Lake Baikal is the deepest and oldest freshwater lake in the world containing about 20% of the world's fresh water. The present state of its contamination with organic pollutants was studied during 1997–1998 by collecting samples of sediments, phytoplankton, Zooplankton, sponges, aquatic plants, algae, muscles of various fish species, eggs of various birds and blubber of seals. Samples were prepared and analysed using GC‐MS for semivolatile priority pollutants on the US EPA list, for the presence of organochlorine pesticides and for PCBs. The results showed that there was pronounced bioaccumulation of persistent organochlorine compounds along the trophic chain, leading to substantial residues of organochlorine compounds in seals (e.g. 0.87–25.3 ppm of p,p'‐DDT in blubber).     

Seals at sea: modelling seal distribution in the German bight based on aerial survey data

The Wadden Sea is an important habitat for harbour seals and grey seals. They regularly haul-out on sandbanks and islands along the coast. Comparably little is known about the time seals spend at sea and how they use the remainder of the North Sea. Yet, human activity in offshore waters is increasing and information on seal distribution in the North Sea is crucial for conservation and management. Aerial line transect surveys were conducted in the German bight from 2002 to 2007 to investigate the distribution and abundance of marine mammals. Distance sampling methodology was combined with density surface modelling for a spatially explicit analysis of seal distribution in the German North Sea. Depth and distance to coast were found to be relevant predictor variables for seal density. Density surface modelling allowed for a depiction of seal distribution in the study area as well as an abundance estimate. This is the first study to use aerial survey data to develop a density surface model (DSM) for a spatially explicit distribution estimate of seals at sea.

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Persistent of Organochlorine Pesticides in the Green Lip Mussel (Perna Viridis) From Marine Estuaries in Thailand

Thailand has benefited from the availability of pest control chemicals for improving agricultural products and in public health like any other developing countries. in order to understand the distribution and contamination in the Gulf of Thailand, a Mussel Watch programme has been set up to monitor trace toxic substances of organochlorine pesticides along the Gulf of Thailand since 1989.

This paper focuses on the concentration of organochlorine pesticides in green lip mussels (Perna viridis) during 1989 to 1996. the mussel samples were used as a biological indicator and analyzed for 23 organochlorine compounds. the highest frequencies of organochlorine pesticide residues in Thailand were found in aldrin, dieldrin and DDTs in all samples and the highest concentration of DDT-isomer were p,p'-DDE and p,p'-DDT during 1989-1990 and 1991. the p,p'-DDE was only found during 1993-1995.

In 1996 the level of the DDT isomer (o,p-DDE) were found in the range of 11-16ppb(ngg^-1 wet weight), HCH isomer (a-HCH) was found ND -1.6ppb(ngg^-1 wet weight) and cis-chlordane found at ND - 3.4 ppb(ngg^-1 wet weight). Other organoichlorine pesticide compounds such as dieldrin, heptachlor, aldrin, endrin and endosulfan isomers were not detected. the detection limit of all organochlorine compounds were 1.3-8.2ppb(ngg^-1 wet weight). Trends of organochlorine pesticide residue in this area were found differently from the previous data during 1989-1991.     

Distribution and bioaccumulation of organochlorine pesticides along the Black Sea coast

Sediment, mussel, and seawater samples were collected three times during 2001–2003 at nine sampling stations along the mid-Black Sea coast of Turkey. The samples were analyzed with GC-ECD for contents of various organochlorine pesticides (OCPs) in the environment. DDT and its metabolites were detected at concentrations significantly above the detection limits. The highest concentrations of DDT metabolites measured in the sediment and mussel samples were 35.9 and 14.0 ng/g wet weight respectively. Considerable levels of aldrin, dieldrin, endrin, heptachlor epoxide, lindane, endosulfan sulphate, and HCB were also detected in the sediment, mussel, or seawater samples. Although these persistent toxic compounds have been banned for some years in Turkey, they may still be used illegally in some regions, contributing to their significant levels in the environment. The biota–sediment accumulation factor (BSAF) estimated for DDT and its metabolites in mussels was 2.9, which is nearly two times higher than the benchmark of 1.7. In spite of such high BSAF values observed for these toxic compounds, their levels in mussels were significantly below the international legal limits recommended by the Food and Agriculture Organization of the United Nations. Edible biota from the waterbodies examined may thus still be considered safe for human consumption at this time. However, as pollutants can biomagnify through the food chain over time, further routine sampling and analysis of biota along the Black Sea coast are warranted in order to better assess the threat of OCPs to public health in the region.     

Satellite telemetry and prey sampling reveal contaminant sources to Pacific Northwest Ospreys.

Migratory behavior can be an important factor in determining contaminant exposure in avian populations. Accumulation of organochlorine (OC) pesticides while birds are wintering in tropical regions has been cited often as the reason for high concentrations in migrant populations. To explore this issue, we satellite tracked 16 Ospreys (Pandion haliaetus) over the period 1996-2003 from breeding sites in British Columbia, Canada, and integrated the results into a database on 15 Ospreys that were satellite tracked over the period 1995-1999, from breeding locations in Washington and Oregon, USA. Data on wintering sites of 31 Ospreys in Mexico and Central America were used for spatially targeted sampling of prey fish. Concentrations of the main organochlorine contaminant, p,p'-dichloro-diphenyl-dichloroethylene (DDE), in fish composites from Mexico ranged from 0.005 to 0.115 nicrog/g wet mass. Significant differences existed among fish families in p,p'-DDE, total dichloro-diphenyl-trichloroethane (sigmaDDT), sigmachlordanes, and total polychlorinated biphenyls (sigmaPCBs). Catfish (family Ariidae) generally had significantly higher levels of DDT metabolites and other organochlorine contaminants compared to other fish families collected. Differences in prey contaminant levels were detected among the collection sites around coastal Mexico, with fish from Veracruz State generally having higher levels of DDT metabolites, sigmachlordanes, sigmaPCBs, and hexachlorobenzene. Eggs collected from 16 nests throughout the Pacific Northwest (nine from British Columbia, seven from Oregon and Washington) where Ospreys had been satellite tagged, showed marked variation in levels of DDT metabolites (p,p'-DDE; range 0.02-10.14 microg/g). Wintering site had no significant effect on contaminant concentrations in sample eggs from those specific Ospreys; rather concentrations of p,p'-DDE, were predicted by breeding sites with highest levels in eggs of Ospreys breeding in the lower Columbia River, consistent with published reports of continued high concentrations of DDT and related compounds in that system.     

Accumulation of Organochlorine Compounds in Oysters (Crassostrea Gasar) of an Estuarine Environment: Case of A Tropical Lagoon in the Gulf of Guinea

As part of a pollution monitoring study, oysters (Crassostrea gasar) were sampled in June 1996, in order to determine the concentrations and distribution of chlorinated hydrocarbons in two stations (near Boulay Island and Riviera Golf) of the Ebrie Lagoon, in the Abidjan area.

The chromatographic analysis of the oven dried samples revealed the presence of PCBs (2.13 to 86.22 ppb or ng/g dry weight), DDE (<0.48 to 169.55 ppb), DDD (<1.04 to 60.27 ppb), DDT (1.43 to 77.81 ppb, lindane (<0.22 to 91.64 ppb), aldrin (<0.30 to 154.1 ppb), endrin (<0.23 to 293.31 ppb) and dieldrin (<0.26 to 199.74 ppb). the results indicated high concentrations in oysters sampled near Boulay Island, due to industrial, agricultural and port activities going on in this area.

Compared to DDD/ΣDDT and DDT/ΣDDT, the DDE/ΣDDT ratios were high indicating old DDT inputs. the ΣDDT/PCBs ratios were higher than 1 illustrated the predominance of organochlorine inputs from agriculture activities. the presence of lindane in both stations illustrated the problem of fishing with toxic products.

Negative correlations found between dry tissue weight and organochlorine compounds concentrations showed that young oysters may concentrate more of these substances. More studies are needed in order to make any conclusions on their bioaccumulation trends.     

Albatross species demonstrate regional differences in North Pacific marine contamination.

Recent concern about negative effects on human health from elevated organochlorine and mercury concentrations in marine foods has highlighted the need to understand temporal and spatial patterns of marine pollution. Seabirds, long-lived pelagic predators with wide foraging ranges, can be used as indicators of regional contaminant patterns across large temporal and spatial scales. Here we evaluate contaminant levels, carbon and nitrogen stable isotope ratios, and satellite telemetry data from two sympatrically breeding North Pacific albatross species to demonstrate that (1) organochlorine and mercury contaminant levels are significantly higher in the California Current compared to levels in the high-latitude North Pacific and (2) levels of organochlorine contaminants in the North Pacific are increasing over time. Black-footed Albatrosses (Phoebastria nigripes) had 370-460% higher organochlorine (polychlorinated biphenyls [PCBs], dichlorodiphenyltrichloroethanes [DDTs]) and mercury body burdens than a closely related species, the Laysan Albatross (P. immutabilis), primarily due to regional segregation of their North Pacific foraging areas. PCBs (the sum of the individual PCB congeners analyzed) and DDE concentrations in both albatross species were 130-360% higher than concentrations measured a decade ago. Our results demonstrate dramatically high and increasing contaminant concentrations in the eastern North Pacific Ocean, a finding relevant to other marine predators, including humans.     

Level of organochlorine pesticide residues in dry fruit nuts

The use of pesticides on cash crops and exportable food commodities had always been a serious concern. Fruits form one of the important constituents of human diet, in that they give one third of the requirement of calories, vitamins, and minerals. This study has been carried out to determine the level of organochlorine pesticides namely HCH, DDT and Endosulfan in raw fruit nuts. Nuts have proteins and high level of fat content. These properties of nuts attract organochlorine pesticides to accumulate. The analysis of organochlorine pesticide residues in commonly used dry fruits like Cashewnut, Walnut, Coconut, Chilgoza, Chironji, Makhana, Resins, Apricot, Almonds, Date palm, Pistachio nut collected from local market of Lucknow India has indicated presence of very low level of HCH (0.007-1.328 mg kg(-1)), DDT(ND-0.140 mg kg(-1)) and Endosulfan (ND-0.091 mg kg(-1)). There are no MRL values established for nuts in the country. This finding is based on a smaller number of samples, which however suggest that the presence of low level of DDT, HCH and Endosulfan might be due to environmental rather than direct exposure.     

Organochlorine levels in human blood from residents in areas of limited pesticide use in Sudan

Ninety-nine human blood samples were collected from the riverine region of northern Sudan and the traditional and mechanized rain-fed areas of western and eastern Sudan, representing areas of limited pesticide use in Sudan. Blood samples were analyzed for organochlorine pesticides by gas liquid chromatography (GLC) followed by electron-capture detection (ECD). p,p′-DDE (a metabolite of DDT), heptachlor epoxide, β-hexachlorocyclohexane (β-HCH), and dieldrin were detected in all locations surveyed. The level of total organochlorine burden was highest in the traditional rain-fed area, followed by the mechanized rain-fed area, and the riverine area. A highly significant correlation was observed between total organochlorine blood burden and the age of the donors (r = 0.608**).     

Accumulation of organochlorine insecticides in the blood of the general population of Nigeria

Gas Chromatographic determination of blood levels of organochlorine pesticides in people of Southern Nigeria is described. Among the compounds detected and quantified were the HCH‐isomers, DDT and its metabolites and dieldrin, the major pollutants being DDT, DDE and the HCH‐isomers. Delta‐HCH, HCB and Endrin were also detected in a few samples. Total DDT (DDT + DDE + DDD) ranged from 0.04–7.24 ppm, total HCH (alpha + beta + gamma) 0.08–5.64 ppm, and dieldrin 0.03–0.28 ppm.     

Chemical contamination and sediment toxicity along the coast of Corsica

Trace metals (Cd, Pb, Cu, Cr, Ni, Co, Zn, Hg, As, Mn, Al, Fe, and Li) and organic compounds (PCBs, PAHs, lindanes, and DDT and its degradation products) were measured in coastal sediment samples from 27 sites in lagoons and along coastal areas of Corsica. An oyster embryo bioassay evaluated the toxicity of sediments from sites in three coastal lagoons (Urbino, Diane, and Biguglia) and the west coast of Cape Corsica. Despite contamination levels generally lower than those in other Mediterranean coastal areas, contamination is found in specific sites in Corsica and includes natural arsenic contamination on the east coast, insecticide pollution (persistent lindane and DDT) in many areas, both cadmium and lead contamination around Sagone, general contamination of both main harbours (Bastia and Ajaccio) and their surrounding areas, and asbestos mining residues in western Cape Corsica. Monitoring development of Crassostrea gigas embryos showed toxic effects at sites near a factory on Cape Corsica, with up to 100% mortality of larvae, and lower levels of toxicity at Sagone (44% mortality) and in the three coastal lagoons (up to 28% mortality). Results of this regional study show the need for further monitoring to understand the environmental issues facing the Corsican coast.     

Bioindikation mit Wanderfalken

Goal and Scope

The Stockholm convention bans 12 prominent persistent organic pollutants (POPs), and the pertinent global monitoring programme recommends birds’ eggs as bio-indicators for the terrestrial food web. As top predators, Peregrine falcons are uniquely suited indicators because of their accumulating power for persistent and lipophilic compounds. On the other hand, the Peregrine falcon as a sentinel species was closer to extinction than other birds of prey. Only unremitting efforts of private omithologists throughout the past four decades in conjunction with the timely banning of organochlorine pesticides like DDT succeeded in saving the Peregrine population of Baden-Wueriternberg from extinction, in contrast to the Peregrine falcons of other German states or other European countries.

Methods

See vd Trenck et al. (2006).

Results and Conclusions

New results confirm the findings of the past long-term bio-monitoring. The main pollutants are PCBs (ca. 20 μg/g) and pp′-DDE (ca. 11 μg/g), the latter contributing >96% of all organochlorine pesticide residues (all concentrations on a dry matter basis). Both substances have followed a slightly increasing trend since 2004. The sum of the polychlorinated diphenyl ethers (PBDE) has fluctuated strongly in the past four years, and in 2006 amounted to 0.6 μg/g (mean without outliers), just as the mercury contamination of the eggs. PCB-156 as the main dioxin-like PCB followed with an average concentration of 0.35 μg/g. Only 10 out of 23 eggs analysed contained hexabromocyclododecane (HBCD) in measurable concentrations; the mean concentration of these eggs was 0.024 μg/g. Tetrabromobisphenol A (TBBA) was detected in all egg samples with a mean of 0.004 μg/g. Due to the many and diverse effects exerted by PCBs; the assessment of this group of compounds, with the aid of European and German regulations for food, proves to be a complex matter, which is currently in a state of flux. There is no doubt, however, that the mean pollution of the Peregrine eggs with toxic dioxin equivalents (WHO TEQ) has reached the no observed adverse effect level (NOAEL) known for chickens and osprey chicks, and the most polluted eggs exceed this threshold considerably. The toxic profile of PBDEs is similar to that of PCBs. They are known to promote tumour growth, to interfere with the thyroid hormone system resulting in toxicity for the neuronal development, to suppress the immune system, and to trigger stress reactions. Tests with highly purified BDE-47 have ruled out dioxin-like effects via Ah-receptor binding for this congener and such effects are therefore very unlikely for the whole class of compounds. At the present time, quantitative criteria for the assessment of the risk posed by PBDEs are not sufficiently reliable, and less so for HBCD and TBBA.

Recommendations and Perspectives

It is necessary to continue the bio-monitoring of POPs and similar pollutants in the terrestrial food web and to establish NOAELs as quantitative criteria for their assessment. Possible sources of dioxin-like PCBs and PCDD/Fs are to be pinpointed, and abatement measures are to be considered where background concentrations are significantly exceeded.     

Long-term variation of organochlorine residues and assemblages of epibenthic organisms in a shallow North Florida (USA) estuary

A 4-year study (1972–1976) determined long-term trends of organochlorine residues (DDT, DDE, DDD, PCB's, mirex) and trawl-susceptible organisms in a shallow, river-dominated estuary in North Florida (Apalachicola Bay, USA). Moderate levels of such compounds were found in various species prior to the restricted use of DDT in 1972. A subsequent precipitous decline in organochlorine besidues was attributed to decreased upland usage, major flushing of the river basin in early 1973, and various factors associated with estuarine function. No mirex was found in sediments or aquatic organisms. Apparently, the half-life of organochlorines is relatively short in this bay system. Various statistical methods were used to test the relationships of different physico-chemical and biological parameters. During the 4-year study period, seasonal river flow fluctuations dominated water color, turbidity, salinity, nutrients (NO₃), chlorophyll a, and the temporal succession of fishes in the bay. Certain long-term trends of fish associations were noted; relative dominance of key fish species declined and stabilized while bay-wide species richness and diversity increased with time. Qualitative changes in species representation determined the long-term pattern of community variability. This was consonant with a distinctive fish fauna during the first year of sampling. The bay anchovy Anchoa mitchilli was dominant during 9 of the first 12 monts of the project; this influenced the time-related changes in community indices. Temporally clustered fish associations reflected the importance of river flow in the estuarine environment. Direct correlation of fish distribution with the rapid disappearance of organochlorine compounds was complicated by aperiodic natural phenomena such as storms and river fluctuations. Population and community trends appeared consistent with other studies showing similar patterns of dominance of stress-resistant fish populations and related changes in community parameters. In this case, the relatively predictable annual succession of fish associations allowed an appraisal of key forcing functions. Due to the high level of seasonal and annual biological variability in this estuary, there were some problems in the application of linear statistical models to the data base. Although the long-term trend of relative species representation is useful as an index of stress, new techniques are needed to analyze extensive field data so that functions such as trophic interactions are included in the estimation of causal relationships. There are indications that such effects could be related to the impact of organochlorine compounds on estuarine systems.     

Chromosome damage in individuals exposed to heavy metals†

Testing the mutagenic activity of environmental pollutants has become an important area of modern environmental science and prophylactic medicine. The most suitable method for short‐term mutagenicity testing on man, at present, are chromosome studies on somatic cells of exposed individuals. Mutation types analyzed by such studies are of high practical relevance as indicator system of genetic damage induced in man under in vivo conditions. A rather large series of such studies has been dedicated to the action of heavy metals on individuals contacted with these metals under therapeutic, ecological or occupational conditions or by intoxication. Lead, cadmium, chromium, nickel, mercury, zinc and other metals as well as their compounds have been under study. Analyses of that kind, of course, are hampered by difficulties with the distinct estimation of the actual load as well as unclear conditions of exposition, e.g. simultaneous exposition to different metals.

Results obtained till now arouse some suspicion of a direct or indirect mutagenic activity in man by certain chromium and platinum compounds, arsenic, mercury, and combinations of lead with other heavy metals (cadmium, zinc, arsenic, antimony, etc.). Life style, above all smoking habits, well may act comutagenic. In most cases, however, mutagenic activity of metals and metal compounds apparently is clearly superposed by their toxic activity. In specific cases, chromosome studies also may contribute to discover sources of ecological exposition and to monitor occupational load by heavy metals.     

DDT in fish from the Bulgarian region of the Black Sea

In spite of a worldwide reduction in the utilization of organochlorine pesticides (OCPs), they are still a problem for the aquatic environment and human health. The Black Sea is still being polluted with persistent chemicals, including OCPs. Aquatic organisms (sprat, scad, bluefish, shad, belted bonito, goby, and black mussel) with different feeding behaviours were sampled on a seasonal basis from the Bulgarian region of the Black Sea, and the concentrations of 13 OCP residues were determined. Although many of the OCPs were not detected in the samples, in all samples 1,1,1-trichloro-2,2-bis(4-chlorophenyl) ethane (DDT) was present mainly in the form of its metabolites 1,1-dichloro-2,2-bis(4-chlorophenyl) ethane (DDD) and 1,1-dichloro-2,2-bis(4-chlorophenyl) ethylene (DDE). Only about 12% of the total DDT was present as the parent compound pp-DDT, which suggests that it was not being used recently in the region. The total DDT concentrations were generally below 150 μg kg^-1 fresh weight, but higher levels—up to 354 μg kg^-1 fresh weight—were also measured for fish species with a high fat content. Between-species differences were observed, even when the concentrations were presented on a fat-level basis. DDT concentrations did not show any significant changes over the 2-yr sampling period. Fish sampled in the northern areas of the Bulgarian Black Sea coast seemed to contain higher DDT levels than those from the southern areas, suggesting a major (historical) influence of the Danube River. For permanent monitoring purposes, the utility of Black Sea gobies and scad should be considered.     

Spatial variability and temporal trends of HCH and DDT in soils around Beijing Guanting Reservoir,China

Spatial variability and temporal trends in concentrations of the organochlorine pesticides (OCPs), hexachlorocyclohexane (HCH) and dichlorodiphenyltrichloroethane (DDT), in surface soils around Beijing Guanting Reservoir (GTR) were studied in 2003 and 2007. Concentrations of the two OCPs in soils around GTR were generally less than reference values set by the Chinese government for the protection of agricultural production and human health. Among the OCPs, β-HCH and p, p′-DDE were the two predominant compounds. This result indicates that the HCH and DDT residues in soils were primarily from historical use. Based on kriging, a spatial distribution of HCH and DDT around the GTR was observed. Spatial variability indicated how HCH and DDT had been applied and been distributed in the past. Between 2003 and 2007, concentrations of HCH and DDT decreased more rapidly in orchard soils than those in fallow soils.     

Characteristics and risk assessment of organochlorine pesticide residues in surface sediments collected at the Qingshitan Reservoir

ABSTRACT

An ultrasonic extraction – gas chromatography – electron capture detector analytical method was used to measure the concentration and types of organochlorine (OC) pesticides in sediment to obtain a better understanding of the characteristics and hidden ecological risks associated with OC pesticide exposure in surface sediment of the Qingshitan Reservoir. Fifteen types of OC pesticides were detected in the sediment, and the sum concentration of these chemicals was in the 149.32–490.19 ng/g range (mean value: 319.39 ng/g). The concentrations of detected OC pesticides occurred in the following order: hexachlorohexanes (HCHs) (mean value: 200.17 ng/g) > DDTs (mean value: 36.92 ng/g) > heptachlors (mean value: 32.74 ng/g) > methoxychlor (mean value: 24.13 ng/g). There was a 100% detection rate for HCH isomers, and their concentrations occurred in the following order: β-HCH > δ-HCH > γ-HCH > α-HCH. β-HCH was the main component of HCHs. Ratios between α-HCH/γ-HCH and β-/(α+γ)-HCH were used to investigate the sources of pollution. Most of the surveyed areas were polluted by lindane, which originated from past pesticide residue usage, and no new inputs of HCHs were found. DDT was the major component of the DDTs, and accounted for 52%–87% of the DDTs. The ratios of (DDE+DDD)/DDT at all sample collection points were less than 1, indicating that degradation rate of DDTs in sediment was low and there was a new input of DDTs in these surveyed areas. The ratio of DDD/DDE was less than 1 at most of the sample collection points, indicating that the degradation of DDT in the sediments primarily took place under aerobic conditions. Comparison of OC pesticide residual levels in the underwater sediment collected at the Qingshitan Reservoir to other states and countries showed the pollution level of these chemicals of the Qingshitan Reservoir was relatively high. The ecological risk was assessed based on guideline values of effects range-low (ERL) and effects range-medium (ERM). The results showed that DDD, DDE, DDTs and endrin residues in the sediment posed a moderate ecological risk, but DDT and γ-HCH showed high ecological risk. These OC pesticides might adversely affect biological systems, and need to be addressed.     

Eier der Flußseeschwalbe (Sterna hirundo) als Indikator für die aktuelle Belastung von Rhein, Weser und Elbe mit Umweltchemikalien

In 1995, common tern (Sterna hirundo) eggs from the big German rivers, the Rhine, Weser and Elbe were collected to study the contamination with organochlorines and mercury. We found distinct differences between the rivers: common tern eggs from the Rhine had higher concentrations of PCBs and HCHs, while eggs from the Elbe had higher residues of DDT, HCB and mercury. Also toxic PCB congeners had higher residue levels in the Rhine. Considering all organochlorines, samples from the Rhine also had the highest concentrations, while those from the Elbe were the lowest. With 5.7 μg×g^?1 fresh weight, the ΖCBs had a level endangering breeding success. Fish eating birds should be used as indicators of the contamination of the rivers with environmental chemicals and should be included in monitoring programmes.     

Levels and distributions of organochlorine pesticides in the soil–groundwater system of vegetable planting area in Tianjin City,Northern China

To study the influence of long-term pesticide application on the distribution of organochlorine pesticides (OCPs) in the soil–groundwater system, 19 soil samples and 19 groundwater samples were collected from agricultural area with long-term pesticide application history in Northern China. Results showed that the composition of OCPs changed significantly from soil to groundwater. For example, ∑DDT, ∑HCH, and ∑heptachlor had high levels in the soil and low levels in the groundwater; in contrast, endrin had low level in the soil and high level in the groundwater. Further study showed that OCP distribution in the soil was significantly influenced by its residue time, soil organic carbon level, and small soil particle contents (i.d. <0.0002 mm). Correlation analysis also indicates that the distribution of OCPs in the groundwater was closely related to the levels of OCPs in the soil layer, which may act as a pollution source.     

广州市蔬菜地土壤重金属污染状况调查及评价

探讨了广州市蔬菜地土壤重金属污染状况,测定了95份土壤样品中铅、镉、铬、砷、汞的含量水平。土壤中铅、镉、铬、砷、汞的含量分别在6.44～153.10mg/kg、0-0.682mg/kg、5.82～101.60mg/kg、0.04～45.36mg/kg、0.01～O.32mg/kg之间。就污染的普遍性而言,铅污染最为普遍,其次是砷污染;就污染的程度而言,镉污染最严重.其次为砷、汞。对比今昔污染变化.广州市土壤污染治理已取得显著成效,但仍需努力。土壤中镉、砷、汞三种元素的变异系数,特别是镉的变异系数较大,这可能预示着点源性污染的存在。