Bioassay technique using seed shrimps for comparative studies regarding the aquatic acute lethality of biodegradable lubricants

To evaluate the environmental load resulting from the spillage of biodegradable lubricants in aquatic systems, a comparative acute lethality test wherein an oil–water interfacial area could be examined was considered. In this study, oleic acid was employed as a model biodegradable lubricant. Measurements of the pH value and dissolved oxygen (DO) level of water during the exposure tests indicate that water degradation depends on the oil–water interfacial area, exposure duration, and water temperature. Furthermore, 72 h acute lethality tests were performed using two types of freshwater ostracods (seed shrimps) as test organisms: the large species Stenocypris hislopi and the small species Cypretta seurati. The longevity of the small species, which was physically more active, was strongly affected by water pollution. During the exposure test, the DO in water was significantly consumed by the degradation of the lubricant floating on it. Water exposed to a lubricant containing copper (Cu) demonstrated strong toxicity even after the recovery of the pH value and DO level by aging. The decrease in the DO level of water and increase in the concentration of metal compounds are dominant factors responsible for the mortality of aquatic organisms.

► Evaluates oil film lethality by using unique test vessel which can control the oil-water interfacial area.
► Adopts two types of ostracods to the aquatic acute lethality tests.
► Evaluates physical activities and viability of the ostracods.
► Suggests a new method for evaluating the toxicity of biodegradable lubricants to aquatic organisms.