Fate of Fenthion in Salt-Marsh Environments: Ii. Transport and Biodegradation in Microcosms

Abstract

The fate of fenthion was examined in laboratory microcosms to describe interaction between sediment and biodegradation in the field. A mathematical model also was calibrated to calculate distribution of fenthion in microcosms. Intact sediment cores, with and without a salt‐marsh plant, Juncus roemerianus (black needlerush), were placed in microcosm vessels to simulate an undisturbed sediment bed of a salt marsh and areas containing Juncus. In a formalin‐sterilized microcosm without plants, fenthion disappeared exponentially from the water column with a half‐life of 105.0 h. Fenthion had a half‐life of 35.5 h in a nonsterile microcosm without plants. In the nonsterile microcosm with plants, the half‐life was slightly shorter, 33.2 h. The sediment was fractionated into 0.5 cm layers. Fenthion was found at greater sediment depths in nonsterile systems than predicted by diffusion and sorption in the sterile microcosm, possibly because of bioturbation. Distribution of fenthion in sediment was not appreciably different between microcosms with and without plants. Fenthion appeared to be biodegraded in the upper (1 to 7 mm) sediment layers.

Modeling the vertical distribution of carbendazim in sediments

“…The fitted diffusion coefficient ( D m = 2.1 × 10 −5 m 2 /d) is close to literature values assuming molecular diffusion only [10,18]. This confirms that turbulent dispersion, as found in the cosm experiments described by Pritchard et al [19] and O'Neill et al [20], did not occur in our model ecosystems with a stagnant water layer. The K f value was a factor of three lower than the value measured in the experiment with suspended solids.…”

Modeling the Vertical Distribution of Carbendazim in Sediments

“…The fitted diffusion coefficient (D m ϭ 2.1 ϫ 10 Ϫ5 m 2 /d) is close to literature values assuming molecular diffusion only [10,18]. This confirms that turbulent dispersion, as found in the cosm experiments described by Pritchard et al [19] and O'Neill et al [20], did not occur in our model ecosystems with a stagnant water layer. The K f value was a factor of three lower than the value measured in the experiment with suspended solids.…”

Degradation Kinetics of Organophosphorus and Organonitrogen Pesticides in Different Waters under Various Environmental Conditions

“…It is important to know the distribution of the pollutant in all the compartments of the aquatic system. The adsorption onto particulates correlated to their log Kow ( 16) may greatly influence the fate of the contaminants as transport (17), bioavailability (18) and degradation are affected. This phenomenon leads to different behaviors: the pesticide may be stressed to a faster degradation (biological or chemical) on these active sites (4), or on the contrary, the pesticide may be protected and exhibit a longer half-life.…”