Heptachlors (heptachlor and heptachlor epoxide) Heptachlor is a pesticide primarily used against soil insects and termites
although it had also been used in controllingmalaria mosquitoes. Heptachlor epoxide is a more stable breakdown product of heptachlor and would normally be assessed together with heptachlor. In the majority (81.5%) shallow groundwater samples, the concentrations of heptachlor were higher than that of heptachlor epoxide, indicating that
there may be some fresh input sources of heptachlor in addition to the historical residues, and the application of heptachlor may have been one of the main fresh input sources of heptachlor in the shallow groundwater of TLR.