Fate of fenthion in salt‐marsh environments: I. Factors affecting biotic and abiotic degradation rates in water and sediment

Abstract

Fenthion (Baytex), an organophosphate insecticide, is frequently applied to salt‐marsh environments to control mosquitoes. Shake‐flask tests were used to study rates of abiotic and biotic degradation of fenthion and the environmental parameters that affect these rates. Water or water‐sediment (500 mg dry weight/L) slurries from salt marshes located along the Northwest Florida Gulf Coast were used. Flasks contained 200 μg fenthion/L, and degradation rates were determined by following decrease of fenthion over time. Hydrolysis and biodegradation in water were relatively insignificant fate processes; fenthion disappeared from flasks containing water, formalin‐sterilized water, or formalin‐sterilized sediment very slowly (half‐life ≥ 2 weeks). The presence of nonsterile sediment resulted in a rapid exponential disappearance of fenthion (half‐life ≥ 3.8 d). Biodegradation was assumed since sterile sediment systems showed a much slower decrease of fenthion, and the production of polar compounds (hexane‐unextractable) from radiolabeled fenthion was greater in the presence of sediment than sterilized sediment. The effect of environmental pH levels (5.0–7.0) on degradation was insignificant. No biotic degradation occurred at low oxygen concentration. An 8°C decrease in incubation temperature decreased the rate of sediment biodegradation 2.5‐fold. Light caused a slight, but significant, increase in the biotic and abiotic degradation rates of fenthion in water. A two‐fold variation in sediment‐mediated degradation was noted among sediment samples from three stations within one field site. Inclusion of whole marsh plants or plant parts increased the disappearance rate of fenthion in test systems.

Mitigation of organophosphate pesticide pollution in agricultural watersheds

“…3). These were within the wide range of values reported in literature (1.8 to 93 days) (Cripe et al, 1989;Mackay et al, 2006). Compared to its biodegradation rate, abiotic hydrolysis of fenthion was much slower with a half-life of 138 days, suggesting that it has a negligible effect on the overall dissipation of fenthion.…”