Research Product

Embryos of the inland silverside, Menidia beryllina, were exposed to the organophosphorus pesticide terbufos at nine combinations of temperature (20°, 25° and 30° C) and salinity (5, 12.5 and 20 o/oo). Nominal exposure concentrations were 12.5, 25, 50 and 100 µg terbufos l-1 with an acetone and seawater control for each temperature/salinity combination. Test durations were temperature dependent and ranged from 5 to 14 days. Endpoints were embryo survival, hatching and percentage of larvae with normal vertebrae. Embryo survival was significantly (a= 0.05) lower in tests conducted at 20° C for all salinities. Salinity affected survival only at combinations of 20 o/oo and 100 µg terbufos l-1. Both temperature and salinity affected the percentage hatch, with the lowest hatching occuring in 20° C tests, and in tests conducted at 20 o/oo. The percentage of larvae with normal vertebrae was significantly (a=0.05) reduced from controls at terbufos concentrations of 25 (7 to 32 %), 50 (44 to 62 %) and 100 µg l-1 (58 to 73 %) for the 3 temperatures tested, whereas salinity showed no significant effect. Anomalies in the development occurred across all temperature and salinity combinations, and were observed at concentrations as low as 12.5 µg terbufos l-1.