The environmental fate of phthalate esters: A literature review

Abstract

A comprehensive and critical review was performed on the environmental fate of eighteen commercial phthalate esters with alkyl chains ranging from 1 to 13 carbons. A synthesis of the extensive literature data on physicochemical properties, partitioning behavior, abiotic and biotic transformations and bioaccumulation processes of these chemicals is presented. This chemical class exhibits an eight order of magnitude increase in octanol-water partition coefficients (K_ow) and a four order of magnitude decrease in vapor pressure (VP) as alkyl chain length increases from 1 to 13 carbons. A critical review of water solubility measurements for higher molecular weight phthalate esters (i.e. alkyl chains ≥ 6 carbons) reveals that most published values exceed true water solubilities due to experimental difficulties associated with solubility determinations for these hydrophobic organic liquids. Laboratory and field studies show that partitioning to suspended solids, soils, sediments and aerosols increase as K_ow increases and VP decreases. Photodegradation via free radical attack is expected to be the dominant degradation pathway in the atmosphere with predicted half-lives of ca. 1 day for most of the phthalate esters investigated. Numerous studies indicate that phthalate esters are degraded by a wide range of bacteria and actinomycetes under both aerobic and anaerobic conditions. Standardized aerobic biodegradation tests with sewage sludge inocula show that phthalate esters undergo ≥ 50% ultimate degradation within 28 days. Biodegradation is expected to be the dominant loss mechanism in surface waters, soils and sediments. Primary degradation half-lives in surface and marine waters range from <1 day to 2 weeks and in soils from <1 week to several months. Longer half-lives may occur in anaerobic, oligotrophic, or cold environments. Numerous experiments have shown that the bioaccumulation of phthalate esters in the aquatic and terrestrial foodchein is limited by biotransformation, which increases with increasing trophic level. Consequently, models that ignore biotransformation grossly exaggerate bioaccumulation potential of higher molecular weight phthalate esters. This review provides the logical first step in elucidating multimedia exposure to phthalate esters.