Long-term sediment bioassay of lead (Pb) toxicity in two generations of the marine amphipod Elasmopus laevis.

摘要

Sediments usually are evaluated for toxicity by measuring mortality in a single cohort of amphipods in either acute (10-day) or chronic (28-day) amphipod bioassays. These tests were developed by the United States Environmental Protection Agency (USEPA) and the American Society for Testing and Materials (ASTM), and do not estimate sublethal effects on reproduction population growth. This study differed from conventional bioassay in three ways: Sublethal reproductive effects were estimated; the test period was 60+ days; and two generations of amphipod offspring (Gammaridae: Elasmopus laevis Smith) were tested. Four test sediment lead levels were investigated; 58 ppm, 118 ppm, 234 ppm and 424 ppm, with sediment containing 30 ppm serving as Control. Statistical analysis of the data indicated that the sex ratio did not depart from 1:1, although counted offspring varied with the number of females in a chamber, and with the ratio of males to females.; Although the current USEPA and NOAA sediment quality guideline for lead indicates that 218 ppm (related to lethality- LD50) will probably have an effect, amphipods in this study showed a strong response to 118 ppm lead, particularly in the second generation which had been exposed during the egg stage: recruitment (via offspring production) into the adult breeding population (28 days) was lower than observed in the Control; longevity (total breeding life) was shorter; fecundity as estimated by Offspring-per-Chamber, Offspring-per-Adult, and Percent Reproductive success was lower than observed in the Control; and sexual maturation was delayed. The number of offspring produced per test chamber, as an inverse function of lead sediment concentration, is best described by a curvilinear exponential equation indicating that significant sublethal population effects are occurring. It was concluded that Elasmopus laevis exposed to 118 ppm of lead and higher could not maintain a population as large as that of the Control. Exposure to toxicants during the egg stage, which occurs in nature, is so crucial that the current guideline of 218 ppm lead must be reconsidered. The advantage of this multiple generation work over previous bioassay methods is its ability to reveal long-term toxicity from exposure to sublethal concentrations of contamination.