Previous studies have shown that freshwater pulmonate snails of the genus Lymnaea are exceedingly sensitive to chronic Pb exposure. An EC20 of <4 μg l-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 ∼1 g) to investigate the mechanisms underlying this hypersensitivity. After 21-day exposure to 18.9 μg l-1 Pb, Ca2+ influx was significantly inhibited (39%) and corresponding net Ca2+ flux was significantly reduced from 224 to -23 nmol g-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 18.9 μg l-1 Pb-exposed group. Results based on direct measurement of Ca2+ influx in 1 g snails gave an influx nearly an order of magnitude higher (750 nmol g-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 Ca2+ concentrations were relatively constant at ∼1100 nmol g-1 over this period. Based on these data, it is estimated that newly hatched snails have net Ca2+ uptake rates on the order of 7600 nmol g-1 h-1. A model was developed integrating these data and measured inhibition of Ca2+ influx rates of 13.4% and 38.7% in snails exposed to 2.7 and 18.9 μg l-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 Ca2+ uptake is the controlling factor in observed Pb hypersensitivity.
- Biotic ligand model
ASJC Scopus subject areas
- Aquatic Science
- Health, Toxicology and Mutagenesis