No abstract

Radiolabeled preparations of the insect growth regulator PH-6040 were evaluated for degradation in a laboratory model ecosystem and after exposure to sheep microsomes, Pseudomonas, soil, and ultraviolet light. The parent compound was found to be moderately stable but was not highly concentrated through food chains or by direct ab-sorption from water. The degradative pathways were almost entirely through cleavage between the carbonyl and amide groups of the urea bridge to give 2,6-difluorobenzamide and 2,6-difluorobenzoic acid, 4-chlorophenylurea, and 4-chloroaniline.The insect growth regulator l-(2,6-difluorobenzoyl)-3-(4-chlorophenyl)urea (PH-6040, OMS-1804) has novel and highly specific activity against a wide variety of insects (Neal, 1974; Wellinga et al., 1973a,b;Jakob, 1973;Van Daalen et al., 1972). The compound is very effective against mosquito larvae, inhibiting growth and development of fourth instar Culex pipiens quinquefasciatus larvae at concentrations of 0.0001-0.001 ppm. The biochemical lesion is suggested to result from the inhibition of chitin synthesis with a resulting defect in endocuticular deposition (Post and Vincent, 1973). As a result, the insect seems characteristically to be unable to complete development. There appear to be no discernible effects on higher animals, and the mouse oral LD50 is in excess of 3000 mg/kg and the LC50 to the guppy >100 ppm. Thus, PH-6040 is a fourth generation insecticide with many attractive properties of selectivity. As it is likely to have extensive usage, we report here on the degradation and environmental fate of PH-6040 in a laboratory model ecosystem, under photochemical stimulation, and in soil.

Radiolabeled benzo-((alpha)-pyrene, benzidine, and vinyl chloride were evaluated in laboratory model ecosystems for environmental fate, degradation pathways, bioconcentration, and food chain accumulation. The comparative effects of microsomal detoxications were evaluated using the inhibitor piperonyl butoxide. The accumulation and bioconcentration of benzo-(alpha)-pyrene and benzidine were closely correlated with their octanol/water partition coefficients and water solubility. Benzo-(alpha)-pyrene as predicted by these parameters was bioaccumulated to substantial levels in several organisms. Vinyl chloride was not accumulated because of its high volatility.

Images FIGURE 1. FIGURE 2. FIGURE 3. FIGURE 5.

A model aquatic ecosystem is devised for studying relatively volatile organic compounds and simulating direct discharge of chemical wastes into aquatic ecosystems. Six simple benzene derivatives (aniline, anisole, benzoic acid, chlorobenzene, nitrobenzene, and phthalic anhydride) and other important specialty chemicals: hexachlorobenzene, pentachlorophenol, 2,6-diethylaniline, and 3,5,6-trichloro-2-pyridinol were also chosen for study of environmental behavior and fate in the model aquatic ecosystem. Quantitative relationships of the intrinsic molecular properties of the environmental micropollutants with biological responses are established, e.g., water solubility, partition coefficient, pi constant, sigma constant, ecological magnification, biodegradability index, and comparative detoxication mechanisms, respectively. Water solubility, pi constant, and sigma constant are the most significant factors and control the biological responses of the food chain members. Water solubility and pi constant control the degree of bioaccumulation, and sigma constant limits the metabolism of the xenobiotics via microsomal detoxication enzymes. These highly significant correlations should be useful for predicting environmental fate of organic chemicals.