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The effect of distribution processes on the isomeric composition of hexachlorocyclohexane in a contaminated riverine system
Berger, M.; Löffler, D.; Ternes, T.; Heininger, P.; Ricking, M. & Schwarzbauer, J.
Abstract
Various factors influence the isomeric composition
of hexachlorocyclohexanes which are released to the
environment. Original compositions in technical mixtures
may vary slightly, but higher shifts are observable for
transfer processes, bioaccumulation and microbial transformation.
Consequently, the isomeric composition in
environmental samples is a superposition of these processes.
In this study, isomeric distributions and concentrations
of hexachlorocyclohexanes were analyzed in
water, sediment, and soil samples of a riverine system
known to be highly contaminated by hexachlorocyclohexanes.
To assess desorption of hexachlorocyclohexanes
from particulate matter to water, batch shaking and percolation
experiments were conducted complementary.
Analyzed samples exhibited total hexachlorocyclohexane
concentrations of up to 2.8 μg/g in sediments and up to
21 μg/L in river water predominated by the α-isomer.
Downstream hexachlorocyclohexane pattern changed
toward δ-isomer domination, while overall hexachlorocyclohexane
concentrations decreased. Desorption experiments
supported the assumption of discrimination by
preferred association of the α- and β-isomers with particulate
matter, showing elevated mobilization of γ-, δ- and ε-hexachlorocyclohexanes
and lower mobilization of the α- and
β-isomers. Soil samples of a riparian wetland exhibited
elevated concentrations of hexachlorocyclohexanes
exceeding 200 µg/g and predominance of α-hexachlorocyclohexanes
in the top soil layer. Subjacent soil layers
showed rapidly decreasing hexachlorocyclohexane concentrations
and an isomeric shift toward the β-isomer. The
assumed preferential mobilization of β-hexachlorocyclohexane
was supported by desorption experiments. This
study demonstrated firstly that transfer processes influence
substantially hexachlorocyclohexane isomer distribution in
the aquatic environment. Secondly, conditions of aging
determine strength of association and remobilization
potential of hexachlorocyclohexane residue down to an
isomer-specific level.
Keywords
Distribution processes; Hexachlorocyclohexane; Isomer-specific; Lindane; Persistent organic pollutant
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