Environmental risk assessment of the insecticide metamidophos in bioassays with four non-target aquatic organisms

The aim of this research was to evaluate the ecotoxicological effect of methamidophos using two formulations of different toxicological class [Monofos®, class Ia (extremely dangerous) and Tamaron®, class Ib (highly dangerous)] on four non-target aquatic organisms: bloodworm Chironomus calligraphus (Goeldi, 1905) (Diptera: Chironomidae), black sea urchin Tetrapygus niger Molina, 1782 (Echinodermata: Arbaciidae), neon tetra Paracheirodon innesi (Rabout, 1940) (Osteichthyes: Characidae); and rainbow trout Oncorhynchus mykiss (Walbaum, 1792) (Osteichthyes: Salmonidae). Both methamidophos formulations evidenced a high risk effect on the aquatic environment, finding effects on larvae of C. calligraphus (Class Ia, LC₅₀ at 48 h = 1.32 mg a.i. L^-1 and Class Ib, LC₅₀ at 48 h = 4.5 mg a.i. L^-1), on fertilization of T. niger (Class Ia, IC₅₀ at 1 h = 1423 mg a.i. L^-1 and Class Ib, IC₅₀ at 1 h = 608 mg a.i. L^-1), on P. innesi (Class Ia, LC₅₀ at 96 h = 20.56 mg a. i. L^-1 and Class Ib, LC₅₀ at 96 h = 10.13 mg a.i. L ^-1) and O. mykiss (Class Ib, LC₅₀ at 96 h = 19.12 mg a.i. L^-1). The sequence of sensibility to methamidophos in both formulations was: C. calligraphus > O. mykiss ≈ P. innesi > T. niger. In addition, two sublethal effects were evaluated on P. innesi, immobilization and strange swimming, and finally an increment of opercular movement in O. mykiss. Risk quotients (RQ) indicated in all cases a high risk of methamidophos towards the aquatic environments.