No abstract

Spinosad is a reduced-risk insecticide with a novel mode of action that provides an alternative to older classes of insecticides such as organophosphates, carbamates and pyrethroids. A comprehensive ecological risk assessment for spinosad use in US cotton crops is presented within a framework of tiered levels of refinement following the guidelines of the US EPA for ecological risk assessments. Toxicity information for a variety of species is documented and utilized, environmental concentrations estimated, and risk characterizations in the form of risk quotients are quantified. Results indicate that spinosad use in cotton does not exceed the most conservative Tier I levels of concern (LOC) values for groundwater, mammals and birds or acute risk to aquatic organisms. Use of very conservative Tier I screening methods resulted in exceeding LOC values for chronic exposure for some aquatic organisms, thus prompting further refinement. When the exposure prediction was refined using less conservative, Tier II mechanistic environmental fate transport models to predict offsite transport and environmental concentrations, chronic risk was not predicted for these species. Spinosad is acutely toxic to bees under laboratory conditions, but toxicity of residue studies and field studies indicate that under actual use conditions the impact on bees is minimal.

Spinosad is a bacterially derived insect control agent consisting of two active compounds, spinosyns A and D. The objective of this paper is to describe the environmental fate of spinosad in aquatic systems. To this end, several studies performed to meet regulatory requirements are used to study the fate and degradation in individual environmental media. Specifically, investigations of abiotic (hydrolysis and photolysis) and biotic (aerobic and anaerobic aquatic) processes are described. Understanding developed from the laboratory-based studies has been tested and augmented by an outdoor microcosm study. Understanding of aquatic fate is a building block for a complete environmental safety assessment of spinosad products (Cleveland, C. B.; Mayes, M. A.; Cryer, S. A. Pest Manag. Sci. 2001, 58, 70-84). From individual investigations, the following understanding of dissipation emerges: (1) Aqueous photolysis of spinosad is rapid (observed half-lives of <1 up to 2 days in summer sunlight) and will be the primary route of degradation in aquatic systems exposed to sunlight. (2) Biotic transformations contribute to spinosad's dissipation, but less so than photolysis; they will be of primary importance only in the absence of light. (3) Spinosad partitions rapidly (within a few days) from water to organic matter and soil/sediment in aquatic systems but not so rapidly as to replace sunlight as the primary route of dissipation. (4) Abiotic hydrolysis is relatively unimportant compared to other dissipation routes, except under highly basic (artificial) conditions and even then observed half-lives are approximately 8 months. Degradation pathways are understood are follows: (1) Degradation primarily proceeds by loss of the forosamine sugar and reduction of the 13,14-bond on the macrolide ring under aqueous photolytic conditions. (2) Degradation to several other compounds occurs through biotic degradation. Degradation under anaerobic conditions primarily involves changes and substitutions in the rhamnose ring, eventually followed by complete loss of the rhamnose ring. Degradation under aerobic conditions was more extensive (to smaller compounds) with the loss of both the forosamine and rhamnose sugars to diketone spinosyn aglycon degradates. (3) Hydrolytic degradation involves loss of the forosamine sugar and water and reduction on the macrolide ring to a double bond at the 16,17-position.

Articles you may be interested inNascent rotational and vibrational distributions in both products of the reaction Zn(41 P 1)+H2O→ZnH(X 2Σ+)+OH(X 2Π) Rotational and vibrational energy distributions of 16OH(X 2Π) and 18OH(X 2Π) produced in the reaction of O(1 D) with H2O and H2 18O Product state distributions in the reaction O(1 D 2)+H2→OH+H: Comparison of experiment with theory Nascent rotational and vibrational population distributions for the reaction 160eD2) + H 2 18 0-+ 160H + 180H have been determined using laser induced fluorescence detection of both OH species. Distributions were corrected for quenching by H2 O. The rotational distribution for v" = 0 of 160H is significantly hotter (19 500 K) than that obtained previously (2600 and 4600 K). In addition, rotational popUlation in v" = 0 of both OH species out to the thermochemical limit (9930 cm -I) cannot be explained by a model in which the OH rotational angular momenta of both fragments must be equal. Further evidence against that model is provided by the preferential population of n (A ') A sublevels, with v" = 0 and 1 having A population ratios of 1.5 and 1.2, respectively. The current data are better explained by an HOOH collision complex formed by insertion of 160(ID2) into the H2 18 0 molecule. The complex probably has a relatively short lifetime, however, because the 160H fragment is more rotationally and vibrationally excited than the 180H fragment. a) Current address: DowElanco, 9001 Building, Midland, MJ 48641.OH was minimized by firing the probe laser coincidently 248

Articles you may be interested inFull characterization of OH product energetics in the reaction of O(1 D 2) with hydrocarbons J. Chem. Phys. 95, 8166 (1991); 10.1063/1.461296 The effect of reagent excitation on the dynamics of the reaction O(1 D 2)+H2→OH(X 2Π)+H J. Chem. Phys. 95, 8038 (1991); 10.1063/1.461284 Reaction dynamics of O(1 D 2)+H2, HD, D2: OH, OD(X 2Π i ) product internal energy distributions J. Chem. Phys. 84, 5365 (1986); 10.1063/1.449947 H+D2 reaction dynamics. Determination of the product state distributions at a collision energy of 1.3 eV J. Chem. Phys. 80, 4142 (1984); 10.1063/1.447242 OH (X 2Π i ) product internal energy distribution formed in the reaction of O(1 D 2) with H2The product OH(Xzn) resulting from the subject reaction has been detected in v" = 2 and v" = 3 with full resolution of N",f", A. " sublevels using LIF spectroscopy in the off-diagonal /1v = -2 sequence bands in the region 385-409 nm. As was noted previously for OH in the v" = 0 and 1 states, strongly inverted rotational distributions were found; in the present case, efficient OH production was observed up to the available exoergicity of the reaction. Production of the 17+ component was again seen to be significantly more probable than that of the 17-. The ratio of summed popUlations in the two observed vibrational levels P(v" = 3)/ P(v" = 2) = 0.39 ± 0.02 is smaller than that observed by other methods; experimental uncertainties in all methods used to date are discussed. The current observations are consistent with a mechanism in which O( ID z ) inserts into the H-H bond to form a highly excited H-O-H complex which then dissociates. No evidence was obtained for a parallel process in which an H atom is directly abstracted by the excited oxygen atom.