Trihalomethane Formation Potential and Concentration Changes During Water Treatment at Mumbai (India)

The treated water at the outlet oftreatment plants and representative servicereservoirs of Mumbai city have been evaluatedfor trihalomethane formation potential in1995–1996. Chloroform, dichlorobromomethane,chlorodibromomethane and bromoform have beenmonitored during monsoon, winter and summer.The levels of chloroform are found above theregulated WHO guideline value of 200 g L^-1 in final water during postmonsoon atGhatkopar (226 g L^-1), Malbar (210.3 g L^-1) and Tulsi (231.26 g L^-1).     

Concurrent Exposure Assessments of Atrazine and Metolachlor in the Mainstem, Major Tributaries and Small Streams of the Chesapeake Bay Watershed: Indicators of Ecological Risk

The goals of this study were to: (1) measure atrazine and metolachlor concentrations during both high and low use periods in the Chesapeake Bay's mainstem/major tributaries, smaller tributaries and representative small agricultural streams during 1995 and 1996; (2) compare these exposure data with toxicity benchmarks for each herbicide to predict ecological risk and (3) use in-stream fish community data collected in the streams to provide supportive data for ecological risk characterization. Spatially, atrazine (<0.10–98 g/L) and metolachlor (<0.10–68 g/L) concentrations were highest in the streams, followed by the small tributaries (<0.10–11 g/L atrazine; <0.10–8.6 g/L metolachlor) with the lowest concentration in the mainstem Bay/larger tributaries (<0.10–0.22 g/L atrazine; <0.10–0.24 g/L metolachlor). Temporally, concentrations of both herbicides were greatest in all three types of habitats in the late spring and early summer. Concentrations of atrazine and metolachlor were very low or non-detectable in all habitats sampled from early August to mid-April. Toxicity benchmarks of 20 g/L for atrazine based on an ecological No Observed Effect Concentration (NOEC) for microcosm/mesocosm studies and an acute 10th percentile of 53 g/L for metolachlor (protection of ninety % of the species) based on laboratory toxicity data were selected to assess annual and seasonal ecological risk. Both of these toxicity benchmarks were conservative estimates of ecological risk designed to protect the trophic group (plants) most sensitive to these herbicides. Based on a comparison of these toxicity benchmarks with two years of exposure data, the ecological risk from both atrazine and metolachlor exposure in the mainstem Chesapeake Bay/large tributaries, small tributaries and representative agriculturally dominated streams was generally judged to be low. During one 72-h stream rain event in 1995, the atrazine toxicity benchmark (20 g/L) was exceeded during part of the event. However, long-term permanent ecological effects are not expected based on the documented recovery potential of the most sensitive trophic group (plant communities) to the concentrations of atrazine reported and the transient nature of the atrazine pulses. Fish communities at the stream sites receiving the highest concentrations of both herbicides were judged to be healthy based on an Index of Biotic Integrity (IBI) developed for Maryland's coastal plain.     

Environmental monitoring of carbaryl applied in urban areas to control the glassy-winged sharpshooter in California

Carbaryl insecticide was applied by ground spray to plants in urban areas to control a serious insect pest the glassy-winged sharpshooter, Homalodisca coagulata (Say), newly introduced inCalifornia. To assure there are no adverse impacts to human health and the environment from the carbaryl applications, carbaryl was monitored in tank mixtures, air, surface water, foliage and backyard fruits and vegetables.Results from the five urban areas – Porterville, Fresno, Rancho Cordova, Brentwood and Chico – showed there were no significanthuman exposures or impacts on the environment. Spray tank concentrations ranged from 0.1–0.32%. Carbaryl concentrationsin air ranged from none detected to 1.12 g m^-3, well below the interim health screening level in air of 51.7 g m^-3. There were three detections of carbaryl in surface water nearapplication sites: 0.125 ppb (parts per billion) from a water treatment basin; 6.94 ppb from a gold fish pond; and 1737 ppbin a rain runoff sample collected from a drain adjacent to a sprayed site. The foliar dislodgeable residues ranged from 1.54–7.12 g cm^-2, comparable to levels reported forsafe reentry of 2.4 to 5.6 g cm^-2 for citrus. Carbarylconcentrations in fruits and vegetables ranged from no detectableamounts to 7.56 ppm, which were below the U.S.EPA tolerance, allowable residue of 10 ppm.     

Characterization of atmospheric dust at Gurushikar,Mt. Abu,Rajasthan

The nature of atmospheric aerosols at Gurushikar, Mt. Abu, Rajasthan where a gamma ray telescope is to be installed, was investigated. Air particulate samples collected on filters were used to estimate the total suspended particulate matter (TSPM) and its elemental composition. The TSPM varied from 31 to 103 g/m³ during January to March 1994. The heighest loads were observed during the months of May and June (80–100 g/m³) and lowest during October (20–60 g/m³). The dust was also examined for size, shape and nature of the mineral matter. The particle sizes varied from 100 m to 5 m. The course particles (>50 m) are irregular shaped quartz grains. Some of the medium size (=50 m) particles were spherical and were highly conducting. These particles were rich in iron content. Correlation coefficients among various elements in the dust showed that it is made up of mainly two components-wind blown ground dust and particulate arising out of wood and coal burning.     

Behaviour and fluxes of trace and toxic elements in creek sediment near Mumbai,India

Studies on marine sediments are extremely important since they act as ultimate sink of anthropogenic pollutants. The present study was conducted near Mumbai city of India to understand andassess the behaviour and fluxes of trace and toxic elements increek sediment. Seven sediment core samples were collected andanalysed for trace and toxic elements such as Fe, Cu, Pb, Zn, Rb and Sr in different sections of the core using EDXRF technique. The fluxes of the elements in each section of the core were calculated using the mass sedimentation rates derivedfrom ²¹⁰Pb dating technique and the sediment density at each location. The estimated depositional fluxes of Fe, Rb and Sr in Zone-1 and Zone-3 are in the ranges of 0.4–0.5% cm^-2yr^-1; 4–6 g cm^-2 yr^-1 and 10–20 g cm^-2 yr^-1 respectively, where as they were about 3–4 times higher in zone-2 for the same elements. The depositionalfluxes of elements Cu (40–60 g cm^-2 yr^-1), Zn (35–43 g cm^-2 yr^-1) and Pb (6–12 g cm^-2 yr^-1) were also found to be higher in zone-2 compared tozone-1 and zone-3 which can be attributed to the release from thenewly developed chemical zone of Thane-Belapur industrial belt.     

A Survey of Trace Metals in Vegetation, Soil and Lower Animal Along Some Selected Major Roads in Metropolitan City of Lagos

The concentration of trace metals (Cd, Cu, Pb and Zn) in a total of 144 samples of grass, soil and lower animal (earthworm, Lybrodrilus violaceous) were collected and analysed for their metallic content. Levels of cadmium ranged from 0.01–0.07 g g^–1; 0.01–0.12 g g^–1 and from trace–0.05 g g^–1 dry weight for plant, soil and animal samples respectively. Mean concentration of copper ranged 0.10–1.48 g g^–1; 0.10–2.90 g g^–1 and 0.01–0.08 g g^–1 for samples in similar order as above. The levels of Pb varied from 0.01–0.14 g g^–1; 0.02–0.23 g g^–1 and from trace–0.07 g g^–1 while that of Zn ranged from 0.19–1.80 g g^–1; 0.51–3.35 g g^–1and 0.01–0.08 g g^–1 also in the same order of samples as mentioned above. Levels of metals in soil samples were higher than the background levels with the exception of Zn but lower than European Union (EU) limits. The results generally revealed the presence of metals in plant and animal samples and metal dynamics up the food chain is highly possible. Acceptable recoveries of the spiking experiment validate the experimental protocol.     

Effect of Common Pesticides Used in the Niger Delta Basin of Southern Nigeria on Soil Microbial Populations

The effects of eleven pesticides on the populations of bacteria, actinomycetes, fungi and protozoa was investigated by treating a garden soil with their recommended rates. The microbial populations were estimated using the standard plate-count technique. Of the ll pesticides investigated, phenylmercuric acetate (agrosan) at 50 g g^-1 inhibited bacterial density the most, i.e. from 4,600,000 to 220 cells g^-1. The pesticides were Pentachloronitrobenzene (PCNB), tetramethylmethylthiuram disulphide (thiram),1- naphthylmethylcarbamate (Vetox 85), 1,2,3,4,5,6-hexachlorocyclohexane (Gammalin 20), phenylmercuric acetate (Agrosan), tetrachloroterephthalic acid (Dacthal), 4-nitrophenyl –2-nitro-4-trifluoromethylphenyl ether (Preforan), 2-ethyl-6-methyl –N-2-methoxy –1-methyl ethyl-chloroacetanide (Dual), Benlate, Brestan and Gramoxone. Pentachloronitrobenzene (PCNB) at 240,000 g g^-1 reduced bacterial population from 4,600,000 to 2,100 cells g^-1, whereas tetramethylthiuram disulphide (thiram) at 100 g g^-1 suppressed it by 2 log orders of magnitude. Soil application of 1-naphthylmethylcarbamate (Vetox 85) at 100 g g^-1 and 1,2,3,4,5,6,-hexachlorocyclohexane (Gamalin 20) at 1,300 g g^-1 repressed the bacterial numbers by 2 log orders of magnitude each. Pentachloronitrobenzene reduced the actinomycetes density from 340,000 to 320 cells g^-1 and completely eliminated all fungal and protozoan propagules from the soil. The Gammalin 20 completely wiped out all the fungi, whereas phenylmercuric acetate totally eliminated all the protozoa and reduced the fungal population from 34,000 to 60 cells g^-1. In general, protozoa and fungi were more susceptible to fungicides than bacteria and actinomycetes. Pentachloronitrobenzene, 1,2,3,4,5,6,-hexachlorocyclohexane and phenylmercuric acetate were toxic particularly to soil microorganisms, whereas the herbicides dacthal, Preforan and Dual were quite harmless in soil at application rates of 0.1, 0.06 and 0.02 g g^-1 respectively.     

Concentrations of Cadmium, Mercury and Selenium in Blood, Liver and Kidney of Common Eider Ducks from the Canadian Arctic

We determined concentrations of selected trace elements inlivers, kidneys and blood samples from common eiders (Somateria mollissima borealis) from the eastern Canadianarctic during 1997 and 1998. Concentrations of totalmercury and organic mercury were generally low in the liversof these birds (less than 6 and 4 g g^–1 dry wt,respectively). Selenium ranged between 11–47 g g^–1 inlivers. Renal cadmium concentrations were among the highestever published for this species (range: 47–281 g g^–1). The regressions of log-transformed concentrations ofthese trace elements in blood samples on those in liver orkidney were significant (all P-values < 0.05) andpositive. However, except for organic mercury (RM ² = 0.83), the co-efficients of determination were low tomoderate (range of R ²: 0.26–0.52), suggesting poorto moderate predictive capability. Furthermore, therelationships between total mercury in blood and liverchanged between 1997 and 1998, suggesting that it would notbe possible to predict consistently, concentrations ofmercury in blood from those in liver based on samples takenin one year. Blood samples can be used to determineconcentrations of these trace elements in common eiders (andprobably other sea duck species as well). The use of bloodsamples is especially warranted when it is undesirable tokill the animal such as when working with rare or endangeredsea duck species or when the objective is to relate traceelement exposure to annual survival rates. However, thepredictive equations developed here should not be used topredict expected concentrations in one type of tissue fromthose in the other.     

Environmental Contaminants in Blood, Hair, and Tissues of Ocelots from the Lower Rio Grande Valley, Texas, 1986–1997

The ocelot (Felis pardalis) isan endangered neotropical cat distributed within asmall range in the Lower Rio Grande Valley (LRGV), inTexas, U.S.A. Studies of the impacts of environmentalcontaminants in wild cats are few. Approximately onefourth of the estimated population (about 100) ofocelots in the LRGV was sampled to evaluate theimpacts of chlorinated pesticides, polychlorinatedbiphenyls, and trace elements on the population. Hairwas collected from 32 ocelots trapped between 1986–1992,and blood was collected from 20 ocelots trappedbetween 1993–1997. A few blood samples were obtainedfrom individuals recaptured two or three times. Tissue samples from 4 road-killed ocelots were alsoanalyzed. DDE, PCBs, and Hg were some of the mostcommon contaminants detected in hair and blood. MeanHg levels in hair ranged from 0.5 to 1.25 g g^-1 dw,Se from 1.5 to 3.48 g g^-1 dw, and Pb from 0.56 to26.8 g g^-1 dw. Mean DDE concentrations in plasma ranged from 0.005 g g^-1 ww to 0.153 g g^-1 ww, and PCBs ranged from 0.006 g g^-1 ww to 0.092 g g^-1 ww. Mean Hg levels in red blood cells rangedfrom 0.056 g g^-1 dw to 0.25 g g^-1 dw. Concentrations of DDE, PCBs, or Hg, did not increasesignificantly with age, although the highestconcentrations of DDE and Hg were found in olderanimals. Overall, concentrations of DDE, PCBs, and Hgwere low and at levels that currently do not pose anythreat to health or survival of the ocelot. This isfurther supported by good reproduction of the ocelotin the LRGV, where adult females averaged about 1.5kittens/litter. Thus, it seems that the current majorthreat to recovery of the ocelot in the LRGV may behabitat loss, although potential impacts of newgeneration pesticides, such as organophosphorus andcarbamate insecticides need further study.     

Organochlorines and selenium in California night-heron and egret eggs

Exceptionally high concentrations of DDE were found in black-crowned night-heron (Nycticorax nycticorax) (geometric mean 8.62 g g^–1 wet wt.) and great egret (Casmerodius albus) (24.0 g g^–1) eggs collected from the Imperial Valley (Salton Sea), California in 1985. DDE concentrations in 14 of the 87 (16%) randomly selected night-heron eggs from six colonies (two in San Francisco Bay, three in the San Joaquin Valley, and one at Salton Sea) were higher than those associated with reduced reproductive success of night-herons (8 g g^–1). In addition, mean shell thickness of night-heron eggs collected from the San Joaquin Valley and from San Francisco Bay during 1982–1984 was significantly less than pre-DDT thickness and was negatively correlated (r=–0.50, n=75, P<0.0001) with DDE concentration. Mean selenium concentration in night-heron eggs from Salton Sea (1.10 g g^–1) was significantly higher than in eggs from three locations in the San Joaquin Valley, and in egret eggs from Salton Sea.     

Monitoring dissolved copper concentrations in Chesapeake Bay,U.S.A.

Dissolved copper and selected water chemistry parameters were monitored for 11 months in Chesapeake Bay, U.S.A. Dissolved copper concentrations in four recreational marinas, a large harbor, two major river systems, and a heavily used shipping canal ranged from below detectable levels to 80 g L^-1 (\-X=11.7 g L^-1). Dissolved copper was detected >91% of the time at five locations. Lowest copper concentrations were found in Potomac River, Baltimore Harbor, Pier One Marina, and C & D Canal (\-X=6–10 g L^-1; slightly higher levels of dissolved copper were found in Choptank River (\-X=12 g L^-1). Highest levels of copper were detected in Port Annapolis, Hartge, and Piney Narrows Marinas (\-X=13–18 g L^-1), with the highest values observed in the study (70 and 80 g L^-1) found in two of these marinas. Copper in the three marinas with highest dissolved copper levels could have been toxic to some of the more sensitive aquatic species. Intensive study of one marina indicated that a likely source of dissolved copper was the recreational boats housed in the marina.     

Pesticides and Nitrate in Groundwater and Rainwater in the Province of Limburg in The Netherlands

The purpose of this study was to investigate the occurrence ofhigh levels of pesticides in groundwater and rainwater in TheProvince of Limburg in The Netherlands. In groundwater samplesin particular the presence of triazines – atrazine, simazine and propazine – was observed; besides these pesticides, dieldrin has also been observed. Atrazine and simazine were found to exceed the groundwater standard of 100 ng L^-1. In the rainwater samples, the presence of 13 of 23 different analyzed pesticides was observed. A number of pesticides werefound in high concentrations; e.g. atrazine (>200 ng L^-1). Two pesticides detected in rainwater (+-HCH and atrazine) were found to exceed the groundwater standard. Seven pesticides in rainwater were found to exceed the target value and three pesticides the maximum tolerable risk value (DDT, heptachlor and heptachlorepoxide A), which are used as ecotoxicological standards in The Netherlands.Nitrate in 15 of 16 analyzed natural springs was found toexceed the guideline value for nitrate in drinking waterof 50 mg L^-1, up to levels of about 200 mg L^-1. Nitrate concentrations in rainwater samples were observed up to 4.5 mg L^-1. A risk analysis of exposure to high pesticide levels in groundwater or rainwater has been performed using the model HESP. For atrazine levels due todeposition of rainwater in two different locations, exceedance of the T.D.I. level of 0.5 g kg^-1 day^-1 based on WHO criteria was observed for children using both an urban and a rural scenario and use of groundwater as drinking water.     

Distribution of heavy metals in plants and fish of the Yamuna river (India)

The distribution of cadmium (Cd), cobalt (Co), chromium (Cr), copper (Cu), iron (Fe), manganese (Mn), nickel (Ni), lead (Pb) and zinc (Zn) in the plants and fish of Yamuna river from Delhi to Allahabad, a distance of about 840 km, at five sampling stations was determined in the year 1981. The results have shown wide variations in the heavy metal levels from one sampling station to the other. The concentrations of Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb, and Zn in the plants (Eicchornia crassipes) were found to be 0.02–0.12, 2.7–21.3, 4.6–64.8, 9.8–114.0, 193.0–1835.0, 380.0–1443.0, 4.4–83.0, 4.8–30.2, and 22.1–356.5 g g^-1 respectively whereas in the fish (Heteropnuestes fossilis) were found to be ND-0.40, 2.3–13.7, 3.7–26.9, 8.33–58.1, 278.3–1108.0, 81.3–213.8, 2.8–32.7, 1.4–12.8 and 101.8–364.8 gg^-1 respectively on dry weight basis.     

Regional monitoring of lead and cadmium contamination in a tropical grazing land site,Thailand

An investigation was carried out to monitor Pb and Cd contamination in grazing land located near a highway. Environmental media at different distances fromhighway (soil, grass, water, cow's forage, fertilizer,manure and milk samples) were collected from three samplinglocations. Soil and grass were characterized by high metalmobility (soil with Pb: 5.25±0.71–14.59±1.17 mgkg^-1, dry mass and Cd: 0.038–0.33±0.04 mg kg^-1, dry mass and grass with Pb: 0.76±0.05–6.62±0.18 mg kg^-1, dry mass and Cd: 0.17±0.01–0.73±0.09 mg kg^-1, dry mass). One-way analysis of variane (ANOVA) was applied to find out the correlation between metal (total and bioavailable) concentrationsin the soil and the distance from roadside. In most cases, the finding showed that plants growing nearer to the highway are usually exposed to more heavy metal accumulations than those awayfrom the highway. In addition, a correlation was established between plant available metal concentrations and plant metaluptake concentrations.Analysis of fertilizer and manure showed considerable amountof metals (fertilizer with Pb: 1.53±0.06 mg kg^-1 andCd: 0.038 mg kg^-1 and manure with Pb: 2.55–3.34 mgkg^-1 and Cd: 0.14–0.31 mg kg^-1). Long termsimultaneous application of fertilizer and manure on thecommercial farm showed higher metal accumulation in the soiland plants than those of co-operative farm Considerableconcentrations of metals (Pb: 1.60–2.94 mg kg^-1 andCd: 0.025–0.19 mg kg^-1) were observed in fodder. The finding clearly demonstrated that there are seasonalvariation in total daily metal intake by individual cow (Pb:109.37 mg day^-1 (dry), 273.47 mg day^-1 (rainy) andCd: 2.02 mg day^-1 (dry), 19.62 mg day^-1 (rainy)).The provisional tolerable weekly intake of heavy metals incows is 390 g Pb and 28 g Cd per kg bodyweight in the rainy season and 156 g Pb and 2 gCd per kg body weight in the dry season. The levels of metals (Pb: 0.014 mg L^-1 and Cd: not detectable) and bio-transferfactor (10^-5–10^-4) in raw milk were found to be well below the Codex Alimentarius Commissions Draft (1997). Ouranalysis revealed that improvements on farm management give significant reduction in elevated levels of Pb and Cdin soil and plants, and however leads to minimize the amountof Pb and Cd in consumed milk.     

Determination of Cadmium and Lead in Different Cigarette Brands in Jordan

Cadmium (Cd) and lead (Pb) concentrations in different cigarette brands sold and/or produced in Jordan were determined by graphite furnace atomic absorption spectrometry (GF-AAS). Average levels of Cd and Pb in different cigarette brands in Jordan were 2.64 and 2.67 g g^{– 1} (DW), respectively. The results obtained in this study estimate the average quantity of Cd inhaled from smoking one packet of 20 cigarettes to be in the range of 3.65–7.30 g. Results suggest that the quantity of Pb inhaled of smoking one packet of 20 cigarettes, is estimated to be 0.74–2.22 g. The concentrations of Cd and Pb in cigarettes were significantly different between cigarette brands tested. Our results were compared with other worldwide studies.     

Long term monitoring of pollutants in eggs of Yellow-legged Herring Gull from Capraia island (Tuscan Archipelago)

Chlorinated hydrocarbons (hexachlorobenzene, lindane, ppDDE, polychlorinated biphenyls) and trace elements (Hg, Se, Cd, Pb) were determined in eggs of Yellow-legged Herring Gull (Larus cachinnans) collected in an island of the Tyrrhenian Sea during the period 1981–1986. PCBs levels vary on the average between 30.4g g^–1 d.w. in 1981 to 56.1 g g^–1 d.w. in 1983. The capillary chromatograms revealed the presence of about 30 somers of PCBs without significant variations in the eggs of the same year; more than 50% of the residues is made up only three isomers: the 22'44'55', the 22'344'5' and the 22'344'55'. Average DDE residues were 7–8 times lower than those of PCBs and declined during the period (from 9.2 g g^–1 d.w. in 1981 to 4.5 g g^–1 d.w. in 1986). Cadmium and lead are present in low concentrations. The average levels of mercury and selenium are around 2–2.5 g g^–1 d.w., and a cumulative correlation, on a molar basis, exists between these two elements.     

Monitoring for 2,4-residues in fish species resident in treated lakes in east-central Ontario 1977–80

Authorized use of 2,4-D by cottage owners in Buckhorn Lake for the years 1977 to 1980 ranged from 124 to 280 kg of active ingredient, annually. This would give predicted average water concentrations of 2 to 4 g L^–1 during the June–July period. However, higher residues were observed in the Lake. Between 1977 and 1980, 353 individual fish, of eight species, were caught for analysis in Buckhorn and Chemong lakes. These fish belonged to eight edible species. Twelve percent of the fish caught during the pre-treatment period (i.e. May), had detectable residues of 2,4-D. Mean residues by species and year ranged from <5 to 30 g kg^–1 2,4-D. In the early post-treatment period (i.e. July), 69% of fish caught had mean residues by species which ranged from <5 to 136 g kg^–1 2,4-D. In the late post-treatment period (i.e. October), 19% of fish caught by year had detectable residues of 2,4-D. Mean residues by species during this period ranged from <5 to 60 g kg^–1 2,4-D. While 15 (i.e. 4%) of the 353 fish and fish composites had 2,4-D above the maximum residue limit of 100 g kg^–1 only six were of edible size.     

Use of a food consumption model to estimate human contaminant intake

A mathematical model is proposed for estimating daily contaminant intake by multiplying three variables related to consumption, from three independent consumption surveys. With lead as an example, the product of the three variables typified the mean and increasing intakes among infants 0–5 months, children 6–23 months and children 2–5 yr of age. Limitations implicit to the approach and the variables were discussed. Daily mean lead intake increased between the three respective age groups, 15, 59, and 82 g lead. When intake was expressed on a body weight basis (g lead/kg BW), the rate of daily lead exposure for children 6 to 23 months (6.1) and 2 to 5 yr (5.6) of age was similar but both were higher than the rate for the 0–5 month infant (2.7 g kg^-1 BW). The 90th percentile daily dietary lead intake for 0–5 month infants was double their mean intake and for children 6 months to 5 yr was one and a half times their corresponding mean intakes. Food sources which contributed to the daily lead intake of the infant differed from those for the two groups of older children.     

Response of Mercury Contamination in Fish to Decreased Aqueous Concentrations and Loading of Inorganic Mercury in a Small Stream

Approximately 250 000 kg of mercury was lost towater and soils at the U.S. Dept. of Energy Y-12 Plantin Oak Ridge, Tennessee in the 1950s and early 1960s. A creek originating within the plant receivedcontinuous inputs of waterborne mercury, predominantlyas dissolved inorganic mercury, from groundwater,streambed contamination, and sump and process waterdischarges to the contaminated storm sewer network.These produce aqueous total mercury concentrations of1–2 g L^-1 in the upper reaches of the stream,decreasing to about 0.1–0.2 g L^-1 in its lowerreaches. A program to reduce mercury concentrationsin the creek identified specific sources (buildingsumps, contaminated springwater seeps, foundationdrains, and contaminated piping) and rerouted wateraround contaminated portions of the drain system orcollected and treated mercury-contaminated waterbefore discharging it. As a result, waterbornemercury concentrations in the creek and total mercuryloading were reduced from 1.8 g L^-1 to0.6 g L^-1 and 100 to 20 g d^-1, respectively, in the last 5 yr.Mean mercury concentrations in fish nearest sourceareas in the creek headwaters decreased at roughly thesame rate as waterborne total mercury concentrationsover the past five years, but at the facility boundarydownstream the decline in mercury bioaccumulation wasmuch less. At sites 5–15 km farther downstream, nodecrease was evident. Dissolved methylmercury tendedto increase with distance downstream in a patterninverse to that noted for its dissolved inorganicmercury precursor.Improvements in water quality and modification ofweirs to allow the passage of fish have resulted inthe establishment of large populations of fish inmercury-contaminated headwater areas previously devoidof fish. It may be that the accumulation, retention,and eventual downstream transport of this reservoir ofbiologically incorporated methylmercury has acted tobuffer against expected reductions in mercury in fishat downstream sites.     

Assessment of lead contamination of the general environment through blood lead levels

More than 2000 blood samples were collected at random from full-time middle school teachers in 9 cities of China and analyzed for lead concentration with strict quality assurance procedures. Questionnaries about the smoking habits, alcohol consumption, residence condition, and fuel used at home were filled out by each person, and information about traffic, and lead concentration in different areas of the environment was also collected as far as possible. The result showed that the geometric mean of blood lead levels of teachers in different cities was ranging between 59–82 g l^–1 among them the lowest levels were found in Nanjing and the highest in Shanghai. The difference between the lowest and the highest value was only 23 g l^–1. Comparing with the results of WHO/UNEP and CEC projects. The overall geometric average blood level in China is lower than in all the other countries except Japan. It indicates that the lead pollution in the general environment of China was not as severe as in the participating countries of WHO/UNEP and CEC projects. This may be attributed by the following factors: The less automobile triffic, the larger proportion of non-leaded gasoline used and the less canned food consumption. Factors influencing the lead levels in blood were also analyzed and the normal value (95% upper limit) of blood lead was assessed to be 160 g l^–1.