Bioaccumulation and Metabolic Fate of Pyrazolate and Its Hydrolysates in Guppies and Short-necked Clams

Ueda, Takashi; Sadakane, Shingo; Yamaoka, Katashi; Nakagawa, Masayuki; Ishida, Mitsuo

doi:10.1584/jpestics.13.85

Cited by 2 publications

References 2 publications

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Herbicides, Inhibiting 4‐Hydroxyphenylpyruvate Dioxygenase (HPPD)

Little¹,

Pallett²

2002

Encyclopedia of Agrochemicals

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4‐Hydroxyphenyl pyruvate dioxygenase (HPPD) is a recently identified herbicide target site. There are currently seven known herbicides that inhibit this target; five commercialized: sulcotrione, isoxaflutole, benzofenap, pyrazolynate, and pyrazoxyfen, and two in the process of being commercialized: mesotrione and benzobicyclon. These herbicides can be classed within three families of 4‐benzoyl‐cyclic aryl or heteroaryl compounds: the benzoyl‐isoxazoles, the benzoyl‐cyclohexanediones, and the benzoyl‐hydroxypyrazoles. As enzymes inhibitors, all share or can give rise to a diketone pharmacophore within their structure. All of these herbicides produce characteristic bleaching symptoms in susceptible species due to the consequences of HPPD inhibition. HPPD catalyzes a complex reaction in which the ketoacid of tyrosine, namely, hydroxyphenylpyruvate (HPPA) is oxidized, decarboxylated, and then rearranged to give 2,5‐dihydroxyphenylacetic acid, or homogentisic acid (HGA). HGA is the precursor of plastoquinone and tocopherols, and the former is a cofactor of phytoene desaturase. This enzyme is key in the biosynthesis of carotenoids, inhibition of which leads to the bleaching symptoms due to the reduction of photosynthetic pigment (chlorophylls and carotenoids) and chloroplast development. The structure and available physicochemical data, toxicology and ecotoxicology data, of these bleaching herbicides is presented, together with a more detailed review of each compound.

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Herbicides, Inhibiting 4‐Hydroxyphenylpyruvate Dioxygenase (HPPD)

Little¹,

Pallett²

2002

Encyclopedia of Agrochemicals

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Bioconcentration, Bioaccumulation, and Metabolism of Pesticides in Aquatic Organisms

Katagi

2009

Reviews of Environmental Contamination and Toxicology

137

102

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The ecotoxicological assessment of pesticide effects in the aquatic environment should normally be based on a deep knowledge of not only the concentration of pesticides and metabolites found but also on the influence of key abiotic and biotic processes that effect rates of dissipation. Although the bioconcentration and bioaccumulation potentials of pesticides in aquatic organisms are conveniently estimated from their hydrophobicity (represented by log K(ow), it is still indispensable to factor in the effects of key abiotic and biotic processes on such pesticides to gain a more precise understanding of how they may have in the natural environment. Relying only on pesticide hydrophobicity may produce an erroneous environmental impact assessment. Several factors affect rates of pesticide dissipation and accumulation in the aquatic environment. Such factors include the amount and type of sediment present in the water and type of diet available to water-dwelling organisms. The particular physiological behavior profiles of aquatic organisms in water, such as capacity for uptake, metabolism, and elimination, are also compelling factors, as is the chemistry of the water. When evaluating pesticide uptake and bioconcentration processes, it is important to know the amount and nature of bottom sediments present and the propensity that the stuffed aquatic organisms have to absorb and process xenobiotics. Extremely hydrophobic pesticides such as the organochlorines and pyrethroids are susceptible to adsorb strongly to dissolved organic matter associated with bottom sediment. Such absorption reduces the bioavailable fraction of pesticide dissolved in the water column and reduces the probable ecotoxicological impact on aquatic organisms living the water. In contrast, sediment dweller may suffer from higher levels of direct exposure to a pesticide, unless it is rapidly degraded in sediment. Metabolism is important to bioconcentration and bioaccumulation processes, as is detoxification and bioactivation. Hydrophobic pesticides that are expected to be highly stored in tissues would not be bioconcentrated if susceptible to biotic transformation by aquatic organisms to more rapidly metabolized to hydrophilic entities are generally less toxic. By analogy, pesticides that are metabolized to similar entities by aquatic species surely are les ecotoxicologically significant. One feature of fish and other aquatic species that makes them more relevant as targets of environmental studies and of regulation is that they may not only become contaminated by pesticides or other chemicals, but that they constitute and important part of the human diet. In this chapter, we provide an overview of the enzymes that are capable of metabolizing or otherwise assisting in the removal of xenobiotics from aquatic species. Many studies have been performed on the enzymes that are responsible for metabolizing xenobiotics. In addition to the use of conventional biochemical methods, such studies on enzymes are increasingly being conducted using immunochemical met...

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Bioaccumulation and Metabolic Fate of Pyrazolate and Its Hydrolysates in Guppies and Short-necked Clams

Cited by 2 publications

References 2 publications

Herbicides, Inhibiting 4‐Hydroxyphenylpyruvate Dioxygenase (HPPD)

Herbicides, Inhibiting 4‐Hydroxyphenylpyruvate Dioxygenase (HPPD)

Bioconcentration, Bioaccumulation, and Metabolism of Pesticides in Aquatic Organisms

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