Factors Influencing the Distribution of Lindane and Other Hexachlorocyclohexanes in the Environment

TLDR

HCH residues are among the most widely distributed organochlorine contaminants, raising environmental and human health concerns that have prompted North American countries to consider a regional action plan and highlighting the need to understand γ‑HCH transformation, especially given high α‑HCH levels in the Arctic. This review investigates whether γ‑hexachlorocyclohexane can transform into other HCH isomers and explores alternative explanations for observed isomer contamination patterns. Laboratory studies demonstrate that γ‑HCH can photoisomerize to α‑HCH, yet field data show little evidence of such transformation and indicate that α‑HCH residues are declining as technical HCH use has ceased.

Abstract

This review examines the potential for γ-hexachlorocyclohexane (HCH) to be transformed into other isomers of HCH. HCH residues are among the most widely distributed and frequently detected organochlorine contaminants in the environment. The potential environmental and human health risks associated with these residues have prompted Canada, the United States, and Mexico to consider the development of a North American Regional Action Plan (NARAP) to assess and mitigate HCH pollution. More information on the propensity of γ-HCH to transform into other isomers is essential to the development of an effective regional management program. The high relative concentrations of α-HCH in the Arctic suggest that γ-HCH may be transformed into other isomers in the environment. Laboratory studies show that significant photoisomerization of γ-HCH to α-HCH is possible. However, field studies do not find evidence for significant isomerization of γ-HCH, and recent environmental samples suggest that α-HCH residues are declining as the use of technical HCH has ended in most parts of the world. Alternative explanations for the patterns of isomer contamination are discussed.