Petroleum and petroleum byproducts are significant contaminants of marine coastal sediments. Their detrimental effects on marine species have been amply demonstrated after oil spills. However, less is known about the effects of lower doses of oil continually entering nearshorc systems from human activities. The present study provides evidence that relatively low doses of waste crankcase oil (WCCO), the predominant petroleum product in runoff and combined sewer overflow discharges, induces measurable sublethal morphological changes in the amphipod Melita nitida Smith, an epibenthic estuarine species. Adults were exposed to 1, 10, and 100 ppm WCCO mixed in sediments. Adult male and female survivorship was not reduced by exposure to these doses. Juveniles maintained at 1 and 10 ppm survived but juveniles maintained at 100 ppm died within 2 days of emergence from the female.

Reproductive females developed abnormal oostegite setae in WCCO. The proportion of females developing abnormalities was directly correlated with the concentration of the WCCO.