Fenitrothion in ponds

Water. Fenitrothion disappeared rapidly from unshaded ponds decreasing to <0.01 pg/L from an initial level of 70 pg/L within 10 to 13 days each year (Fig. 1). In shaded water fenitrothion levels decreased more slowly reaching 0.01 to 0.02 pg/L by about 17 days each year (Fig. 2). Half-lives of fenitrothion calculated from first-order decay curves (In concentration vs time (days)) were significantly greater in shaded treatments each year (Table 2). The half-lives observed were within the range found elsewhere in field studies in ponds and small lakes (1). 

Table II. Half-lives (t 1/2) of fenitrothion and degradation products in pond water - Year 1 and 2.

Aquatic plants and fish. Duckweed rapidly accumulated (r4C)-fenitrothion from the water column and maximum concentrations were observed after 5 to 10 days post-treatment in both years (Table III). The levels observed at 5 days represented concentration factors (BCFs) of 754 and 688 in shaded and unshaded exposures, respectively (Year 2), based on total radioactivity in water and plants. Concentrations in duckweed decreased to <10% of the maximum by 35 days each year. Levels of radioactivity in the plants were not significantly different in shaded and unshaded conditions. This differs from results of Weinberger et al (4) who observed 3-fold greater concentrations of ( 4C)-fenitrothion in Elodea densa in field microcosms under lighted compared to darkened conditions. Duckweed did not grow well under shaded conditions and by 17 days the density of the plant was about 10% of that in the unshaded pond. 

Air. Concentrations of fenitrothion in air sampled 10 cm above treated ponds were highest in the first 24 hours post-treatment (Table III). GLC analysis of the extracts from polyurethane foam traps indicated that only fenitrothion was present. The levels of fenitrothion were generally higher above shaded ponds. This was expected because the polyethylene shelter reduced wind movement over the water surface which would dilute the observed concentrations. Recently Mallet and Volpe (7) reported the detection of ng/L levels of AF as well as fenitrothion in air samples collected near treated areas in New Brunswick (Canada) however, the source of AF was not clear from their study. 

The accountibility of (14C)-fenitrothion was considerably reduced by 21 days. In Year 1 estimates of total fenitrothion in water were obtained by use of extractable radioactivity which was low by Day 5 resulting in low estimates of the total fenitrothion in water. Another source of error could be greater deposition of fenitrothion on sediments on the sides of the ponds which is not taken into account by sampling the pond bottom. This has been observed with pyrethroid insecticides in similar outdoor ponds... 

Residues of fenitrothion in fathead minnows were reported by Malls and Muir (19) following treatment of small ponds. Bioconcentration factors were 42 and 54 at 24 hours post treatment, as compared with predicted steady state bioconcentration factors of 146 (Table I). Following actual forest spraying Lockhart et al. (20) reported 13.7 pg fenitrothion per gram in fish taken from a stagnant pond in the spray zone. The peak water concentration observed was 75.5 pg/L, and so the bioconcentration factor was at least 180. Similarly, Lockhart et al. (21) found maximum fish residues of 4.28 pg/g from the same area sprayed two years later, and in this case the peak water concentration was 22.8 pg/L, with a calculated bioconcentration factor of 190. 

Mails and Muir (19) treated an experimental pond with fenitrothion and observed that fenitrothion levels in duckweed changed relatively little from 1 to 10 days after treatment. The averages of radioactivity (as fenitrothion) in the plants over that interval were 17480 and 18229 pg/kg in shaded and sunlit ponds respectively, on a dry weight basis. During the period after treatment water content of radioactivity declined continuously, but "average" values taken as the means of initial and 10-day samples were 43 and 37 pg/L for the same ponds. Calculated bioconcentration factors were therefore 406 and 492 fold for the shaded and sunlit ponds. The rate constant ratio (Table III) indicates a steady state prediction of 24 on a wet... 

Marshall, W.K., and J.R. Roberts. 1977. Simulation modelling of the distribution of pesticides in ponds. In J.R. Roberts, R. Greenhalgh, and W.K. Marshall (Eds.), Proceedings of a symposium on fenitrothion. The long-term effects of its use in forest ecosystems. National Research Council of Canada, Publication No. 16073. 

The objective of this study was to follow the dissipation of fenitrothion under conditions resembling a stagnant forest pond. Fenitrothion has frequently been detected at pg/L concentrations in stagnant waters following aerial spray operations since... 

The shaded and unshaded ponds were each treated on two consecutive years (July, 1979 and again in June, 1980) with fenitrothion at a rate of approximately 165 g/ha similar to commonly used rates of aerial application (1). The formulation consisted of fenitrothion (175 mg Year 1 and 163.4 mg Year 2 technical grade), 11(C-fenitrothion (100 pCi Year 1 90 pCi Year 2), 33 mg Aerotex 3470 (Texaco Canada Ltd.) and 34 mg Atlox (Atlas Chemical Co.) in 500 mL water. The formulation was stirred into the upper 10 cm of the water column with a metal rod. 

Table I. Water chemistry parameters and light intensity in outdoor ponds following fenitrothion treatment - Year 1.

The cover over the shaded pond was removed at 17 days post-treatment in the first year of the study due to damage from a rain storm. Removal coincided with an unexplained increase in fenitrothion concentrations (Fig. 2). This increase was not observed in Year 2 when the shade was removed at the same time (Fig. 2). It is possible that disturbance of the water and sides of the ponds may have released sediment and plant-associated fenitrothion back into the water column, however, levels of degradation products did not increase proportionally. 

Figure 1. Disappearance of fenitrothion and degradation products in unshaded pond water following addition of the insecticide each year.

The effect of shading an outdoor pond for the first 17 days after addition of fenitrothion was to increase the half-life of the insecticide by about 50%. Despite a 30-fold reduction in light intensity, however, the decline in insecticide residues in water was rapid dropping from 70 jtg/L to about 0.01 jxg/L by 17 days. Shaded conditions decreased the quantities of other products and MNP (but not AF) that were formed however no major products unique to shaded or unshaded conditions were identified. 

Maquire, R.J., Hale, E.J. (1980) Fenitrothion sprayed on a pond Kinetics of its distribution and transformation in water and sediment. J. Agric. Food Chem. 28, 372-378. 

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