Haematological parameters as predictors of blood lead and indicators of lead poisoning in the black duck (Anas rubripes)

The validity of various haematological parameters as indicators of blood lead concentration and lead poisoning in the black duck (Anas rubripes) is discussed. Elevated (> 40 microg dl(-1)) blood lead (PbB) levels were recorded in 41% of the 229 wild birds examined. No correlation was found between PbB concentration and haematocrit. Zinc protoporphyrin (ZPP) was positively correlated with PbB. Haemoglobin, delta-aminolevulinic acid dehydratase (ALA-d) activity and non-activated/activated ALA-d ratios were negatively correlated with PbB. The minimum PbB levels at which these parameters were affected varied greatly. ZPP and haemoglobin were relatively insensitive to PbB concentrations; whilst ALA-d activity and ALA-d ratio were influenced by PbB concentrations of < 5 microg dl(-1). Log(10) ALA-d ratio was more strongly correlated with PbB (r = -0.953) than log(10) ALA-d activity (r = -0.914) and the predictive validity (% false -ve and +ve predictions) of the ratio method was higher. The high individual variability in ALA-d activities at low PbB levels was greatly reduced by the use of the ALA-d ratio method. The ALA-d ratio method proved the most efficient for screening black duck for lead poisoning in the field.     

The use of kriging to estimate monthly ozone exposure parameters for the Southeastern United States

This paper explores the feasibility of (1) using kriging to predict the monthly mean of daily 7-h mean (0900-1559) O3 concentrations, (2) using kriging to estimate the per cent of hourly mean O3 concentrations equal to or greater than 0.07 ppm (137 microg m(-3)) for a specific month, and (3) developing a quantitative relationship between the monthly mean of the daily 7-h (0900-1559) average O3 concentration and the monthly number of hourly concentrations > or = 0.08p ppm (157 microg m(-3)). We found that kriging can be used to estimate the (1) monthly mean of daily 7-h mean O3 concentrations and (2) the percentage of hourly concentrations for a given month > or = 0.07 ppm when sufficient spatial coverage was available. However, the per cent > or = 0.07 ppm parameter exhibited much greater relative variability than the monthly 7-h exposure index. A strong statistical association was found between the monthly number of occurrences > or = 0.08 ppm and monthly 7-h mean concentrations above 0.05 ppm (98 microg m(-3)). Because of the variability that cumulative indices, such as the monthly percentage of hourly concentrations > or = 0.07 ppm , exhibit from site to site, it appears that whether kriging techniques or mathematical regressions are used to estimate the number of elevated O3 hourly concentrations above selected thresholds, large uncertainties associated with the predicted values will exist. These large uncertainties will make it difficult to accurately estimate vegetation effects caused by ambient levels of O3. However, if a generalized quantitative relationship between repeated occurrences of hourly mean concentrations > or = 0.07 ppm or > or = 0.08 and vegetation effects can be developed, it may be possible, using kriged monthly values accompanied with confidence intervals, to identify those areas where vegetation may be at risk. However, before it will be possible to implement such an approach, researchers will have to better quantify the relationship between realistic O3 exposures and vegetation effects.     

Bank voles as monitors of environmental contamination by heavy metals. A remote wilderness area in Poland imperiled

Concentrations of heavy metals (Cd, Pb, Cu, Zn, Fe) were determined in the tissues of bank voles collected in polluted forest sites in southern Poland and in Bia?owieza National Park. The highest cadmium concentrations were found in livers (0.9-12.8 microg g(-1)) and kidneys (3.2-29.6 microg g(-1)), whereas the lowest were in bones (0.2-0.9 microg g(-1)). The lead concentrations found in kidneys and bones ranged from 9.5 to 40.0 microg g(-1). The ranges of zinc, iron and copper concentrations in the tissues of animals were: 137-343 microg g(-1), 206-1017 microg(-1) and 12.0-73.8 microg(-1), respectively. Some of the differences between the levels found in various sites were statistically significant.     

Radium-226 levels and concentration ratios between water, vegetation, and tissues of ruffed grouse (Bonasa umbellus) from a watershed with uranium tailings near Elliot Lake, Canada

Radionuclide levels measured in bone, muscle, kidney and liver tissues, gut contents and diet items of 47 grouse from the Serpent River drainage basin, containing uranium (U) tailings at Elliot Lake, and from control areas in Ontario, showed variation by site and tissue. The mean level of 226radium (Ra) in bones of grouse sampled from Elliot Lake (28.5 mBq g(-1)) was higher than that in bones of birds from a distant control site near Sudbury, Ontario (8.0 mBq g(-1)) but similar to the value in a local control population (28.1 mBq g(-1)). Birds from Mid- and Low-Serpent River basin populations (with 17.1 and 17.7 mBw g(-1), respectively) did not differ from local or distant control populations; muscle, liver and kidney had lower 226Ra concentrations, which did not differ significantly among populations. Levels of 226Ra in the crop contents and intestine did not differ significantly by site and were similar to those of food items consumed by the birds. Stomach content values were higher in birds sampled in Elliot Lake and at the local control site than in those taken at the distant control site; birds sampled downstream from Elliot Lake did not differ from distant controls in this regard. Levels of 232thorium (Th) and 230Th were below detection limits (0.1 microg g(-1) and 5.0 mBq g(-1), respectively) in bone, muscle and liver tissue in two grouse with elevated levels of 226Ra. Other radionuclides were measurable in some tissues: 238U in bone at 0.4 microg g(-1), in muscle to 0.2 microg g(-1), in liver to 1.0 gmg g(-1.), 228Th was found only in muscle (8.0 mBq g(-1)), 210poloniuim (Po) was found in bone, muscle and liver (maxima: 24.0, 7.0, 16.0 mBq g(-1)) with the exception of one muscle sample; 210lead (Pb) was detected in only one liver sample (50.0 mBq g(-1)). Environmental levels fell within ranges previously reported at the sites, or at similar locations elsewhere. Leaves of trembling and largetooth aspen growing in the basin had mean 226Ra levels of 14.8 and 52.7 mBq g(-1) (dry weight) respectively, and fungal material carried up to 215.4 mBq g(-1) (air-dried), with some variation by site. River and lake waters sampled near the U tailings had 118.1 mBq litre(-1) of dissolved 226Ra; at the distant control site the value was 12.1 mBq litre(-1). The concentration ratios (CR) between bone of grouse collected at the Elliot Lake sites and trembling and largetooth aspen leaves were 1.38 and 1.09 (fresh weight basis); from other diet items and to other tissues the values were less than unity. Bone tissue: water ratios, based on dissolved 226Ra levels, ranged to 30.89. People eating grouse from the study area are unlikely to consume radionuclides in excess of limits currently established by Canadian regulatory authorities.     

Evaluation of cadmium, copper, zinc, and iron concentrations and tissue distributions in the benthic crab, Dorippe granulata (De Haan, 1841) from Tolo Harbour, Hong Kong

The distributions of copper, zinc, iron, and cadmium among the tissues of Dorippe granulata were determined. The highest copper concentrations were found in the haemolymph (c. 53 microg ml(-1)) while the highest iron concentrations occurred in the gills (c. 720 microg g(-1) dry weight) and the highest zinc concentrations in the exoskeleton (c. 200 microg g(-1) dry weight). By comparison, concentrations of the non-essential metal, cadmium, were low in all tissues (mean = 10 microg g(-1) dry weight). The highest value was recorded from the midgut gland of a female crab (18.5 microg Cd g(-1) dry weight). Concentrations of copper, zinc, and iron were positively correlated with tissue-hydration levels. Such a relationship was not found for cadmium. The findings are discussed with regard to trace-metal levels found in temperate and tropical brachyurans from clean and polluted localities.     

Airborne PBDEs in specialized occupational settings, houses and outdoor urban areas in Greece

Airborne polybrominated diphenyl ethers (PBDEs) were measured in workplaces, homes and urban outdoor air in Greece. The geometric mean concentrations of total PBDEs (sum of 19 congeners) in offices (205pgm(-3)), internet cafes/computer rooms (127pgm(-3)) and computers/electronics shops (85pgm(-3)) were significantly higher than those in furniture stores (12pgm(-3)), homes (8pgm(-3)) and outdoor air (18pgm(-3)). The daily inhalation intake of PBDEs estimated for the employees of the four occupational settings ranged from 0.2 to 1.4ngday(-1) and it was significantly lower than the expected dietary intake ( approximately 77ngday(-1)). Although inhalation generally represented a small fraction of the overall daily exposure to PBDEs ( approximately 1%), the results from a heavily contaminated office (10 848pgm(-3) of total PBDEs) indicated that the intake from this route (65ngday(-1)) may, in some extreme cases, be as important as diet.     

Distribution of trace element pollutants in a contaminated ecosystem established on metalliferous fluorspar tailings. 3: fluoride

High total soil fluoride (10 000 microg g(-1)) in the metalliferous fluorspar tailings was reflected by elevated concentrations in standing live vegetation (300-1000 microg g(-1)); plant roots (c. 6000 microg g(-1)); plant litter (c. 4000 microg g(-1)); total body concentrations of invertebrates (400-4000 microg g(-1)) and the small mammals Microtus agrestis (120-360 microg g(-1)) and Sorex araneus (140-250 microg g(-1)). Seasonal changes in the standing live vegetation and the availability of soil fluoride to plants are discussed. Seasonal changes in total body concentrations of the small mammals were related to the age structure of the populations as well as dietary levels. In the small mammals, the concentration ratios were < 0.5 at the tailings dam and > 1.1 at the control site, indicating that both species were able to regulate fluoride accumulation at the higher levels of intake. Soft tissue concentrations were, as expected, very low compared to the hard tissues but, still, were generally significantly higher at the tailings dam compared to the control site. Evidence of dental fluorosis was found in Microtus agrestis, but not Sorex araneus.     

Elemental uptake by edible herbs and lettuce (Latuca sativa)

The total concentration of toxic elements (aluminum, cadmium, chromium and lead) and selected macro and micro elements (iron, manganese, copper and zinc) are reported in six leafy edible vegetation species, namely lettuce, spinach, cabbage, chards and green and red types of Amaranth herbs. Although spinach and chards had greater than 125 mv of iron, both the amaranthus herbs recorded > than 320 microg g(-1) dry weight. In both the spinach and chard species, the Mn and Zn levels were appreciable recording > 225 microg g(-1) and 150 microg g(-1) dry weight, respectively. Aluminum concentrations were (in microg g(-1) dry weight) lettuce (10), cabbage (11), spinach (167), chards (65), amaranthus green (293) and amaranthus red (233). All the micro and macro elements and the toxic elements (Ni, Cr, Cd and Pb) elements analyzed, were below the recommended maximum permitted levels (RMI) in vegetables. Further the elemental uptake and distribution of the nine elements, at three growth stages of the lettuce plant grown on soil bed under controlled conditions are detailed. In the soil, except for iron (16%), greater than 33% of the other cations were in exchangeable form. Generally in the lettuce plant, roots retained much of the iron (> 224 microg g(-1)) and aluminum (> 360 microg g(-1)), while leaves had less than 200 microg g(-1) of iron and 165 microg g(-1) of Al. Although the concentrations of elements marginally decreased with growth, the lettuce leaves had significant amounts of Mn (30 microg g(-1)), Zn (50 microg g(-1)) and Cu (3.6 microg g(-1)). Some presence of lead in leaves (2.0 microg g(-1)) was noticed, but all the toxic and other elements analyzed were well below the RMI values for the vegetables.     

The long-term environmental behaviour of strontium and barium released from former mine workings in the granites of the Sunart region of Scotland, UK

The concentrations of strontium and barium have been measured in water, sediment and the shells of mussels (Mytilus edulis) from a river system in the Sunart region of Scotland, UK. The aim was to establish the fate and mobility of these elements, which are slowly being released from old mine workings on the Strontian granites. Enhanced strontium (1500-2000 microg l(-1) and 250-290 microg l(-1)) and barium concentrations (316 microg l(-1) and 83 microg l(-1)) were found in the waters originating from the two mine drains studied. Both element were also found at significant levels in the river sediments taken from the vicinity of each drainage site (Sr: 225 microg g(-1) and 120-125 microg g(-1); Ba: 1380 microg g(-1) and 126-170 microg g(-1)). The data suggests that the sediments are acting as a reservoir for these group II cations from where they become distributed throughout the river system. Strontium is found to be incorporated into the shells (3.16-3.46 microg g(-1)) and pearls (3.57 microg g(-1)) of the blue mussel, located at the estuarine margin some 10 km downstream, at values close to the maximum expected (3.3% by weight of the calcium content). The study presents a view of the fate of barium and strontium in a river system over a prolonged period of time. As such it provides valuable information for studies that seek to model the impact of the accidental release of barium and strontium (including the important radionuclide 90Sr) into the environment.     

Carbonyl compounds in the urban environment of Athens,Greece

The concentration levels of 15 selected carbonyl compounds in 62 samples were determined at two sites in Athens basin from June to December 2000. Formaldehyde was the most abundant species (0.05-39 microg m(-3)), which comprised from 22% to 37% of the total measured compounds, followed by acetaldehyde (4.32-49 microg m(-3)), acetone/acrolein (0.64-198 microg m(-3)) and butanal (0.79-140 microg m(-3)). The mean formaldehyde/acetaldehyde and acetaldehyde/propanal molar ratios were calculated. No significant seasonal differences were observed for all the carbonyls. Photochemical production was found to weigh upon atmospheric levels for 83-93% in summer days, dropping below 33% in the winter. The importance of formaldehyde and acetaldehyde as a source of hydroxyl radicals in Athens was also assessed.     

Toxicity of fenvalerate to caddisfly larvae: chronic effects of 1- vs 10-h pulse-exposure with constant doses

Episodic pollution events such as runoff or spraydrift can lead to a short-term (few hours) contamination of aquatic ecosystems with pesticides. So far, different short-term exposures with respect to long-term effects have not been studied. In the present study, caddisfly larvae, typical for agricultural streams (Limnephilus lunatus Curtis, 2nd and 3rd instar) were exposed for 1- vs 10-h to three different equivalent doses (microg h) of fenvalerate. After transfer into an artificial stream microcosm with pesticide-free water, chronic effects were observed over 240 days. Comparison of 1- and 10-h exposure revealed that 1-h contamination leads to stronger effects. The differences were significant for the sublethal endpoints emergence pattern and dry weight of adults (ANOVA, Fisher's PLSD; P < 0.05). In terms of exposure dose, the difference between 1- and 10-h exposure equals a factor of 6 as a mean of all endpoints studied. The following significant effect levels for the 1-h exposure were obtained for the different endpoints investigated: reduced emergence success and production at 0.1 microg l(-1), temporal pattern of emergence at 0.001 microg l(-1), dry weight of adults at 0.01 microg l(-1).     

Blood-Pb and hair-Pb levels in donor-matched samples

Lead concentrations in blood and scalp hair of 200 school boys, aged 6-8 years, were measured by electrothermal atomic absorption spectrometry. The mean blood-Pb concentration was 6.8 microg dl(-1) and the mean hair-Pb concentration was 9.7 microg g(-1) (dry weight). These values are well within the normal range for the respective tissues, indicating that the children studied are presently at relatively low risk from environmental lead pollution. A correlation analysis carried out on the data failed to show any statistically significant correlation (r = 0.13, p < 0.05) between the blood-Pb and hair-Pb concentrations.     

Formaldehyde levels in air and wet precipitation at Mexico City, Mexico

Formaldehyde concentrations in ambient air and in rain water were measured at the University of Mexico, Mexico City. Air samples were taken twice a day, from 9:00 to 13:00 h and from 13:00 to 16:00 h local time from July to December 1985. Rain water was collected on daily bases from July to October, i.e. during the rainy season. The ambient air mean value was 24.4 x 10(-3) ppmv for morning hours, while the afternoon mean value was 18.5 x 10(-3) ppmv. The formaldehyde concentration in wet precipitation ranged from 0.10 to 0.80 mg liter(-1) (3.3 to 26.6 micromoles liter(-1)) 0.41 mg liter(-1) (13.7 microoles liter(-1)). A comparison of the results of this study with some measurements made at remote maritime sites, rural and urban areas, indicated that the formaldehyde levels in the atmosphere and rain water of Mexico City are among the highest reported in the literature, including the data reported by Grosjean (1982) for Los Angeles, California, during severe photochemical pollution conditions.     

Factors influencing the total mercury and methyl mercury in the hair of the fishermen of Kuwait

Total and methyl mercury (MeHg) levels in the hair of fishermen are described anticipating that they represent the critical group for dietary exposure. One-hundred human hair samples were collected from fishermen (Egyptians: age range 25-60), living in Doha Fishing Village, Kuwait. Thirty-five additional samples were taken from a control group working in a local construction company (age range 26-35). Overall mean concentrations in the hair of the population of fishermen are 4.181+/-3.220 and 4.025+/-3.130 microg g(-1) for total and MeHg, respectively. The equivalent values for the control are 2.617+/-1.404 and 2.556+/-1.391 microg g(-1) for total and MeHg, respectively. MeHg concentrations are strongly correlated to those of total Hg ( [Formula: see text], [Formula: see text] ) and MeHg concentrations in human hair are unrelated to age and duration of residence in Kuwait but show a positive correlation with the quantity of fish consumed. Levels of Hg in hair also show a tendency to increase in those who prefer to eat the entire fish, including the heads. In general, the concentrations of total and MeHg in fishermens' hair are twice the WHO 'normal' level (2.0 microg g(-1)) but are still less than the WHO threshold level (10.0 microg g(-1)). The results also show that grey hair contains undetectable amounts of Hg and therefore does not reflect individual exposure to this contaminant.     

Bioaccumulation of cadmium by the freshwater isopod Asellus aquaticus (L.) from aqueous and dietary sources

Experiments were conducted to determine the kinetics and relative importance of aqueous and dietary uptake of cadmium by the freshwater isopod Asellus aquaticus (L.). Test animals were exposed during 30 days to aqueous Cd in a continuous flow system (exposure levels: 0.2 - 10 microg litre(-1)) and kept on a diet of previously contaminated Elodea sp. (range of Cd concentrations: 2-350 microg g(-1), dry weight). Preceding semi-static experiments on dosage-control of the dietary factor revealed a rapid uptake of Cd by Elodea, with relatively high concentration factors (CF), which ranged from 4.8 to 5.5 (dry weight log (CF) after 16 days). For Asellus uptake from water appeared to be the predominant route. Highly significant bioconcentration of cadmium from water was observed in the animals, even at exposure levels below 1.0 microg litre(-1). In the various treatments, direct uptake from water accounted for 50-98% of the body burdens after 30 days exposure. The experimental results were described with a first order one-compartment bioaccumulation model. Model parameter estimates (mean +/- standard error) were obtained for rate constant of uptake (560 +/- 110 day(-1)), rate constant of elimination (0.032 +/- 0.017 day(-1)) and assimilation efficiency of Cd uptake from food (1.1 +/- 0.7%). The (dry weight) bioconcentration factor (BCF) and bioaccumulation factor (BAF) for extrapolated steady state conditions were estimated at 18 000 (BCF) and 0.08 (BAF). Experiments conducted at two different pH levels (5.9 versus 7.6) revealed no significant effects of pH on the uptake of aqueous Cd by the isopods. The results are discussed in relation to their potential significance to the field situation.     

Alimentary lead intake of adults in Thuringia/Germany determined with the duplicate portion technique

The daily lead intake in Germany in 1996 was studied using the duplicate portion technique. The study was carried out in four towns in Thuringia (Jena, Ronneburg, Rositz, Steudnitz), in which volunteers collected all foods and beverages over 7 consecutive days. The mean lead content of consumed food and beverages was 66 and 55 microg/kg dry matter for women and men, respectively; the average lead intake was 19 microg/day for both, women and men. In relation to body weight (b.w.) the intake for women was 283 ng/kg and for men 242 ng/kg b.w. These values are well below the WHO limit. An oral lead exposure of the adult population of Thuringia/Germany can be excluded.     

Persistent organochlorine residues in soils from tropical and sub-tropical Asian countries

Soil samples from paddy fields, uplands, and urban areas (gardens and roadsides) collected from Vietnam, Thailand, and Taiwan were analysed to determine the residual levels of persistent organochlorine compounds such as DDTs, HCHs, and PCBs. DDT concentration in soil samples from Vietnam were found to be highest, with a mean value of 110 ng g(-1), and were followed by those in Taiwanese soils with a mean value of 20 ng g(-1). HCH concentrations were highest in soil samples from Vietnam (a mean value of 4.8 ng g(-1)) and were followed by those from Taiwan (a mean value of 1.4 ng g(-1)). Concentrations of PCBs were found to be highest in Taiwanese soil samples, with a mean of 95 ng g(-1). Interestingly, relatively high concentrations of PCBs in rural cultivated-soil samples from Vietnam were recorded with a mean value of 25 ng g(-1), probably suggesting PCB release from different kinds of weapons used during the Second Indochina war. The lowest concentrations of DDTs, HCHs, and PCBs were obtained in soil samples from Thailand, with mean values of 8.3 ng g(-1), 0.4 ng g(-1), and 2.7 ng g(-1), respectively.     

Toxicity of crude oil to the mayfly, Hexagenia bilineata (Ephemeroptera: Ephemeridae)

Effects of crude oil on survival and behavior of the mayfly Hexagenia bilineata were evaluated in laboratory studies. Mayfly nymphs were exposed to the water soluble and oil residue fractions of crude oil. Mayfly survival was not reduced by a 96-h exposure to either the water soluble fraction or the oil residue mixed with sediment. However, significant mortality did result from a 21-day exposure to oil residue mixed with sediment at concentrations as low as 500 microg g(-1). Survival was also reduced after a 21-day exposure to oil-contaminated sediments (1905 microg g(-1)) collected 6 weeks after a crude oil spill in the Chariton River, Missouri. In a behavioral test measuring habitat exclusion, organisms did not avoid contact with sediment containing oil residue (50-800 microg g(-1)). Collectively, results from these studies indicate that exposure to oil residue in sediment will reduce survival of H. bilineata in the laboratory and may reduce survival in the environment for 6 weeks or more after an oil spill.     

Age- and sex-based comparative distribution of selected metals in the scalp hair of an urban population from two cities in Pakistan

Concentrations of Cu, Zn, Pb and Ni in the scalp hair of male and female donors, with an age range of 6-60 years, were determined by ICP atomic emission spectroscopy. The donors were drawn from the densely populated city of Lahore and the relatively less-populated capital city of Islamabad for comparative evaluation of the metal levels in relation to age, sex and location. Linear regression analyses and correlation between paired metals indicated a positive correlation between Cu and Zn for both sexes ( [Formula: see text] ) and between Pb and Ni ( [Formula: see text] ) for males and females of Lahore. Metal concentrations varied between the two cities and the two sexes. The highest mean concentration was found for Zn at 180.5 microg g(-1) for males and 202.4 microg g(-1) for females from Lahore, while for counterparts from Islamabad the values were 105.2 microg g(-1) and 206.6 microg g(-1). Copper showed an identical mean concentration (20.8 microg g(-1)) in the hair of both males and females from Lahore; however, relatively lower mean concentrations (7.7 and 10.8 microg g(-1)) were observed for donors from Islamabad. Mean Pb concentrations in hair of male donors from Lahore and Islamabad were 9.4 and 7.0 microg g(-1), respectively; in female groups the concentrations were 14.3 and 5.7 microg g(-1), respectively. Ni showed the lowest concentration range (4.3-4.5 microg g(-1)) of all the four metals for subjects from Lahore, and this was higher than the corresponding range (2.0-3.2 microg g(-1)) for subjects from Islamabad. The findings are discussed in relation to the available data from the literature.     

Chronic toxicity of tributyltin to development and reproduction of the European freshwater snail Lymnaea stagnalis (L.)

Chronic toxicity, growth and reproduction were measured in the freshwater gastropod Lymnaea stagnalis exposed to waterborne bis(tri-n-butyltin) oxide (TBTO) over a range of four nominal concentrations (0-10microg TBTl(-1)). Egg development was completely inhibited at 10microg TBTl(-1), whilst abnormal embryonic development was observed at 1microg TBTl(-1). For the solvent control and the 0.01microg TBTl(-1)treatment group, normal development of L. stagnalis was observed. Survivorship of hatchlings was significantly reduced by TBT at 1microgl(-1) while inhibition of shell growth of L. stagnalis was also observed at this concentration. The data were used to determine intrinsic growth rates (r) using two theoretical approaches (the Euler-Lotka equation and a Leslie Matrix). Both approaches showed that survival, fecundity and population growth rate were reduced at 1microg TBTl(-1). Interestingly, at 0.01microg TBTl(-1) snails showed a higher fecundity and growth rate than in the solvent control. The TBT concentration at which the r would equal zero (ECr(0)) and the population NOEC (No Observed Effect Concentration) were estimated. The population NOEC was defined as either the lower 95% confidence or lower 95% pointwise percentile limit of the ECr(0). Values obtained using the two different approaches were similar and thus a geometric mean was calculated to obtain a final representative population NOEC value for L. stagnalis of 2745ng TBTl(-1). The present data together with chronic toxicity TBT data for freshwater organisms, obtained from peer-reviewed literature, were used to construct a species sensitivity distribution (SSD). A predicted no effect concentration was then derived from the SSD (hazardous concentration at 5%, i.e., HC5 or 95% protection level). This SSD was compared with the SSD derived from saltwater species datasets. The HC5 value for saltwater species (3.55ng TBTl(-1); lower confidence limit: 1.93ng TBTl(-1)) was significantly lower than that for freshwater species (30.13ng TBTl(-1); lower confidence limit: 9.23ng TBTl(-1)), indicating that saltwater species are probably more susceptible to TBT than their freshwater counterparts.