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Philip H Howard

Publications and source records attributed to Philip H Howard.

2 recordsLinked to original sources

A review of quantitative structure-activity relationship methods for the prediction of atmospheric oxidation of organic chemicals.

Organic compounds are chemically transformed in the troposphere by reaction with photochemically generated oxidants that include hydroxyl radicals, nitrate radicals, and ozone. The reaction rates are a measure of atmospheric persistence and are necessary for developing environmental exposure assessments. Since relatively few experimentally measured rate constants are available, environmental risk/exposure assessors must estimate degradation rates. Rates can be predicted through use of quantitative structure-activity relationships (QSARs). QSAR methods are described for estimating reaction rates with hydroxyl radicals, nitrate radicals, and ozone. QSAR accuracy and limitations are also discussed.

Air Pollutants↗

Recent developments in broadly applicable structure-biodegradability relationships.

Biodegradation is one of the most important processes influencing concentration of a chemical substance after its release to the environment. It is the main process for removal of many chemicals from the environment and therefore is an important factor in risk assessments. This article reviews available methods and models for predicting biodegradability of organic chemicals from structure. The first section of the article briefly discusses current needs for biodegradability estimation methods related to new and existing chemicals and in the context of multimedia exposure models. Following sections include biodegradation test methods and endpoints used in modeling, with special attention given to the Japanese Ministry of International Trade and Industry test; a primer on modeling, describing the various approaches that have been used in the structure/biodegradability relationship work, and contrasting statistical and mechanistic approaches; and recent developments in structure/biodegradability relationships, divided into group contribution, chemometric, and artificial intelligence approaches.

Artificial Intelligence↗