Effects of tributyltin and diazinon on the intertidal marine harpacticoid copepod tigriopus japonicus

The intertidal zone plays an important role in the ecology of coastal waters by providing marine organisms a place to feed, grow, and spawn. Because the organisms that inhabit these areas may be contaminated and adversely affected by pollutants, an assessment of the impact of pollutants on intertidal zone organisms is needed. Tributyltin and diazinon are environmental pollutants that have been detected in coastal waters and are well known to be highly toxic to aquatic organisms. In this study, we performed acute and life-cycle toxicity tests with an intertidal organism, the copepod Tigriopus japonicus. The 48 h-LC50 (i.e., the concentration that killed half the organisms in 48 h) values for tributyltin revealed that nauplii (48 h-LC50; 3.72 μg/L) were more sensitive to tributyltin than adult males and gravid females (48 h-LC50; 7.16 and 7.69 μg/L, respectively). In contrast, the 48 h-LC50 values for diazinon showed that adult male and gravid females (48 h-LC50; 164 and 216 μg/L, respectively) were more sensitive to diazinon than nauplii (48 h- LC50; >1400 μg/L). Life-cycle toxicity tests with tributyltin or diazinon showed that tributyltin and diazinon reduced the fecundity of T. japonicus under the experimental conditions. The lowest concentrations of tributyltin and diazinon that reduced the fecundity of T. japonicus were found to be 1.6 μg/L and 15.7 μg/L, respectively. Although the risk of exposure to tributyltin and diazinon individually in the environment was estimated to be negligible, a mixture of the two might exert adverse effects on T. japonicus in the intertidal zone.