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Hexachlorocyclohexanes
Hexachlorocyclohexanes (HCHs) are persistent organic pollutants (POPs) found throughout the world in air, water, soil, sediment and biota. HCHs include eight isomers of which five dominate the commercial mixture technical HCH, a widely used post WWII pesticide, that typically contains 60-70% alpha-, 5-12% beta-, 10-12% gamma-, 6-10% delta-, and 3-4 % epsilon-HCH.
NOAA's Mussel Watch Project began monitoring for gamma-HCH (lindane) in 1986 and has analyzed over 1,600 samples of bivalve mollusks at more than 280 sites in US coastal waters including Alaska , Hawaii and Puerto Rico . Gamma-HCH is declining at some sites and increasing at none. Since 1995, nearly 450 bivalve tissue samples have been analyzed for alpha-HCH. However, there are insufficient years of data (6 years minimum) to evaluate alpha-HCH temporal trends.
Mussel Watch sites range in latitude from 18 ° N ( Puerto Rico ) to 61 ° N ( Alaska ). The majority of declining gamma-HCH trends occurred along the Northeast Coast between 40° and 44° N latitude. Most of the eleven Alaskan sites exceed the 85th percentile of the alpha-HCH concentration. HCH concentrations were significantly correlated with several variables and although the correlations were weak the results provide further evidence for long-range transport and global fractionation of HCHs along a latitudinal gradient.
References
Society of Environmental Toxicology
and Chemistry (SETAC) poster