Chronic toxicity of lead to three freshwater invertebrates--Brachionus calyciflorus, Chironomus tentans, and Lymnaea stagnalis

Effect of Na, Ca and pH on simultaneous uptake of Cd, Cu, Ni, Pb, and Zn in the water flea Daphnia magna measured using stable isotopes

The present study investigates the effects of Na(+), Ca(2+) and pH on the kinetics of Cd, Cu, Ni, Pb, and Zn uptake in Daphnia magna at low exposure concentrations measured using a stable isotope technique. Using experimental data the uptake rate constants were calculated for each metal individually on the basis of total metal concentrations. The copper uptake was not significantly affected by variations in chemical composition of the test medium. Calcium had a suppressing effect on the uptake of Cd, Ni, Pb and Zn. Specifically, Cd and Ni uptake rate constants decreased with increases in calcium concentrations from 0.1 to 2.5mM. The uptake of Zn and Pb was significantly suppressed only at 2.5mM Ca. The effect of sodium was less clear. There was no effect of varying sodium concentrations on the Ni uptake rate constants. Cd and Pb showed an increase in uptake rate constants at elevated sodium concentrations (2-8mM Na(+) for Cd and 8mM Na(+) for Pb). A bell-shaped response on increasing Na(+) concentrations was observed for Zn with a maximum value of uptake rate constant at the middle value (2mM Na(+)). Variation in pH of the medium affected Cd, Ni and Zn uptake processes. When Daphnia were exposed to acidic conditions (pH 6), the Cd and Ni uptake rate constants were the highest, while similarly low values were observed at neutral and basic conditions. In contrast, the uptake rates of Zn were linearly increasing with increasing pH of the medium.

High net calcium uptake explains the hypersensitivity of the freshwater pulmonate snail, Lymnaea stagnalis, to chronic lead exposure

Previous studies have shown that freshwater pulmonate snails of the genus Lymnaea are exceedingly sensitive to chronic Pb exposure. An EC20 of <4microgl(-1)Pb for juvenile snail growth has recently been determined for Lymnaea stagnalis, which is at or below the current USEPA water quality criterion for Pb. We characterized ionoregulation and acid-base balance in Pb-exposed L. stagnalis (young adults approximately 1g) to investigate the mechanisms underlying this hypersensitivity. After 21-day exposure to 18.9microgl(-1)Pb, Ca(2+) influx was significantly inhibited (39%) and corresponding net Ca(2+) flux was significantly reduced from 224 to -23nmolg(-1)h(-1). An 85% increase in Cl(-) influx was also observed, while Na(+) ion transport appeared unaffected. Finally, a marked alkalosis of extracellular fluid was observed with pH increasing from 8.35 in the control to 8.65 in the 18.9microgl(-1) Pb-exposed group. Results based on direct measurement of Ca(2+) influx in 1g snails gave an influx nearly an order of magnitude higher (750nmolg(-1)h(-1)) than in comparably sized fish in similar water chemistry. Under control conditions, specific growth rate in newly hatched snails was estimated at 16.7% per day over the first 38-day post-hatch and whole body Ca(2+) concentrations were relatively constant at approximately 1100nmolg(-1) over this period. Based on these data, it is estimated that newly hatched snails have net Ca(2+) uptake rates on the order of 7600nmolg(-1)h(-1). A model was developed integrating these data and measured inhibition of Ca(2+) influx rates of 13.4% and 38.7% in snails exposed to 2.7 and 18.9microgl(-1)Pb, respectively. The model estimates 45% and 83% reductions in newly hatched snail growth after 30-day exposure in these two Pb-exposed groups. These results compare well with previous direct measurements of 47% and 90% reductions in growth at similar Pb concentrations, indicating the high net Ca(2+) uptake is the controlling factor in observed Pb hypersensitivity.

Effects of dietary Pb on accumulation, histopathology, and digestive enzyme activities in the digestive system of tilapia (Oreochromis niloticus)

With the increasing occurrence of dietary lead (Pb) contamination in aquatic environment, threat of the dietary Pb toxicity to aquatic organisms attracted more attention. In this study, after being exposed to dietary Pb at concentrations of 0, 100, 400, and 800-microg/g dry weight for 60 days, the groups of tilapia (Oreochromis niloticus) were sacrificed and sampled to analyze the effects of dietary Pb on accumulation, histopathology, and digestive enzyme activities in tissues of the digestive system. The results showed that the Pb accumulation in tissues increased with the dietary Pb concentrations. Moreover, Pb accumulated in sampled tissues in the following order: intestine > stomach > liver. By observation of liver histological sections in optical microscope, lesions could be detected in the Pb-contaminated groups. It was also demonstrated that the inhibitory effect of dietary Pb on digestive enzyme activities was dietary Pb concentration dependent. Different degrees of inhibition of enzyme activities were exhibited in sampled tissues. It was indicated that digestive enzyme activities in the digestive system might be considered as the potential biomarkers of dietary Pb contamination in tilapia.

Reduction of growth and haemolymph Ca levels in the freshwater snail Lymnaea stagnalis chronically exposed to cobalt

The ecological risk assessment and the development of water-quality criteria for Co are currently still hampered by insufficient knowledge about the toxicity of Co to freshwater organisms. A relevant group of organisms, for which no toxicity data with Co are available, is the class of the herbivorous pulmonate freshwater snails, which fulfil a pivotal role in the consumption and decomposition of aquatic plants and epihyton. We measured the growth rate of the pond snail Lymnaea stagnalis chronically exposed for 28 days to a series of Co concentrations. The no observed effect concentration (NOEC) and the lowest observed effect concentration (LOEC) for growth rate were 26 and 79 microg Co/L, respectively. Growth rate of snails exposed to 79 microg Co/L and higher concentrations was more impaired in the final 2 weeks of exposure than in the first 2 weeks of exposure. The reduced growth rate at 79 microg Co/L was accompanied by a reduced concentration of Ca in the haemolymph at the end of the exposure. Possible mechanisms of toxicity of Co to snail growth were suggested to be an impairment of Ca uptake and homeostasis and/or feeding inhibition. Although additional research is needed to investigate the relative importance of these mechanisms, as well as the interrelatedness between them, the toxicity data currently presented can assist in risk assessment and water-quality criteria development.

Interaction effects of multi-metal solutions (As, Cr, Cu, Ni, Pb and Zn) on life history traits in the rotifer Plationus patulus

While many studies have determined toxicity of single heavy metals, few have addressed the combined effects of multiple elements at different concentrations. In order to estimate how metal mixtures affect population dynamics of freshwater rotifers, we exposed Plationus patulus to environmentally relevant concentrations and combinations of arsenic and five heavy metals (Cr, Cu, Ni, Pb and Zn) for 8 days. The life-history parameters, intrinsic rate of increase (r), relative cumulative reproduction (RCR), mortality ratio, mictic ratio, fertilization ratio, and number of deformed offspring were used as endpoints. Exposures were repeated 4 times and considered as blocks in the experimental design. Differences between treatments were evaluated through ANOVA and LSD mean analysis. The combined presence of As, Cu, Ni, Pb, and Zn in different concentrations produced a variety of changes in the population dynamics of P. patulus. However, only Cr produced a significant element*environment interaction. The presence of Cr leads to significant decreases in the intrinsic rate of increase and increased mortality ratio in multi-metal environments. The population growth (as r) decreased from 0.25 to -0.16 due to Cr (10 microg/L) interaction with the remaining elements, and values 0.16-0.12 were observed in treatments containing high levels (50 microg/L) of Cr. Mortality ratio increased from 0.066 to 0.822 due to Cr (10 and 50 microg/L) interactions with the remaining elements at high concentrations. Responses of this basal consumer to metal mixtures will provide insights into how aquatic food webs and their constituent organisms can be altered by anthropogenic inputs like heavy metal contamination.

Acute and chronic copper toxicity to a saltwater cladoceran Moina monogolica Daday

The objective of this study was to evaluate the sensitivity of a saltwater cladoceran Moina monogolica Daday to copper toxicity. Acute and chronic toxicity tests were conducted according to the American Society for Testing and Materials (ASTM) guidelines. The 24- and 48-h LC(50)s and their 95% confidence intervals (CIs) were calculated as 154.21 (135.50-182.05) microg Cu/L and 106.07 (99.77- 112.36) microg Cu/L , respectively, based on measured copper concentrations. When compared with different phyla or classes of estuarine organisms, M. monogolica had moderate sensitivity and was suitable to be used as an indicator organism in the Changjiang estuary. Eight end points of longevity, number of broods, brood size, total reproduction, time to first brood, intrinsic rate of natural increase (r(m)), net reproductive rate (R(0)), and mean generation time (T) used to evaluate chronic effects were affected at chronic copper concentrations. Comparisons of chronic effects showed that toxicity mechanisms of dissolved copper are different from those of dietary exposure. The EC(20)s, EC(50)s, and their 95% CIs of end points were calculated using linear regression equations. The geometric mean generated the maximum-acceptable-toxicant concentration of 6.74 microg Cu/L between the no-observed-effect concentration of 5.06 and the lowest-observed-effect concentration of 8.99 microg Cu/L for brood size, total reproduction, r(m), and R(0), and 12.1 microg Cu/L between 8.99 and 16.29 microg Cu/L for longevity and number of broods as the end points, respectively. The EC(20) of R(0) appeared to be the most sensitive at 3.82 microg Cu/L among the end points. Results showed that aquatic organisms were possibly negatively affected at sites of higher copper concentrations in the Changjiang estuary. Further research is needed to evaluate the direct or indirect effects of copper more comprehensively to protect aquatic organisms and their habitats in the Changjiang estuary.