LIFE-TABLE EVALUATION OF SEDIMENT-ASSOCIATED CHLORPYRIFOS CHRONIC TOXICITY TO THE BENTHIC COPEPOD, AMPHIASCUS-TENUIREMIS

A partial life-cycle experiment was conducted to assess chronic effect s of sediment-associated chlorpyrifos, an organophosphate pesticide, o n a marine, benthic copepod population. The static-renewal experiment was initiated with 4 treatments including control, 13 replicates per t reatment with one female (bearing first clutch of eggs) per replicate. No males were added because one fertilization is sufficient for sever al clutches. Once weekly, all replicate chamber contents (10-ml cultur e tubes with 1.5 mi of sediment and 5 mi of seawater) were sieved and enumerated to determine survival and fecundity. Surviving adult female s were placed back into chambers with newly spiked sediments. This pro cess was repeated for 7 weeks until all initial females were dead or r eproduction had ceased for at least two weeks. Survival and fecundity data were then used to determine population dynamic parameters such as r (intrinsic rate of natural increase) for each treatment. Results re vealed a chronic toxicity response with significant population effects (p < 0.05) in all pesticide treatments versus the control; concentrat ions that represent 7-32% of the 96-hr LC(50). The control treatment h ad an r value 26-52% higher than the pesticide treatments. This transl ated into a control population rate increase of up to twice that of pe sticide treatments. In addition, significant reductions in weekly and total fecundity were found in all chlorpyrifos treatments. Based on th ese results, usage of population parameters with benthic copepods allo ws for an integrative measurement of population effects from chronic e xposure to sediment-associated contaminants.