Standard water exposure as well as sediment toxicity tests were performed in Monsanto laboratories and on-site at the Saginaw River in a mobile bioassay trailer to develop sediment toxicity tests and assess the hazard of Pydraul® 50E (P50E) when sorbed to sediments. Sediment samples were collected from five river stations and tested in the field. Sediment concentrations of P50E, an aryl phosphate ester hydraulic fluid, were determined for each site. The site furthest upstream contained the lowest level and was used as a control site. Both acute and chronic tests were performed with the sediments and with control sediments spiked with P50E using the midge Chironomus tentans and the daphnids Daphnia magna and Ceriodaphnia affinis.

The results indicate that field toxicity tests conducted with river sediments and river water agreed within a factor of two with those obtained in the laboratory using spiked soils and well water. Acute sediment toxicity tests performed with C. tentans and D. magna together provided a rapid screen of the acute toxicity of Saginaw River sediments and P50E spiked on river sediments. Chronic sediment tests with Ceriodaphnia affinis provided a rapid sensitive measure of the toxicity of the Saginaw River sediments. Benthic species diversity in the Saginaw river and C. affinis reproduction in sediment toxicity tests were correlated (r = 0.59) and decreased as function of distance downstream from the control site. They did not correlate well with P50E (r = −0.18) concentrations that ranged from <0.01 to 11.31 mg/kg. Margins of safety calculated for these sediment concentrations ranged from 13 to 39 000 indicating that the potential of this chemical to impact Saginaw River benthic organisms is low.