Acute and sublethal toxicity of naphthalene and three methylated derivatives to the estuarine copepod, Eurytemora affinis

The bi-cyclic aromatic hydrocarbon naphthalene (N) and its alkylated derivatives 2-methylnaphthalene (MN), 2,6-dimethylnaphthalene (DMN) and 2,3,5-trimethylnaphthalene (TMN) were used to investigate possible relationships between increased methylation and toxicity during acute high level and chronic low level exposure experiments using the calanoid copepod Eurytemora affinis Poppe. The 24-h LC₅₀ levels determined indicated an approximate twofold increase in toxicity per methyl group addition: N-3798 μg/litre; MN-1499 μg/litre; DMN-852 μg/litre and TMN-316 μg/litre. Low level chronic exposure of E. affinis to the various naphthalenes in sea water concentrations of about 10 μg/litre for the duration of their adult life (maximum twenty-nine days) resulted in significant reductions in length of life, total numbers of nauplii produced and mean brood size. Exposure to all the naphthalenes at this level (10 μg/litre) resulted in reduced rates of egg production which were, on average, about 50% of those of control animals. Results are discussed in relation to previous work on the fate and effect of petroleum hydrocarbons in marine copepods.