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Environmental impact

Heptachlor was used extensively until the 1970s as a broadspectrum insecticide on a wide variety of agricultural crops, with the major use on corn. It also had nonagricultural uses including seed treatment, home and garden uses, and termite control.
It has a low vapour pressure, low water solubility and is hydrolysed in surface water to 1hydroxychlordene, and a halflife in water estimated at one day. But, experimentally when heptachlor was added to river water and exposed to sunlight, only 25% remained after a week, this corresponds to a halflife in water of 3.5 days. When released directly into water, it adsorbs strongly to suspended and bottom sediment.
The experimental value for the Henry's law constant is suggesting that heptachlor partitions somewhat rapidly volatilize to the atmosphere from surface water. Volatilization from soil particles is also possible and is an important mechanism of transport of heptachlor from land surfaces. In the vapour phase photooxidation is the key degradation process. The atmospheric halflife for heptachlor reacting with hydroxyl radicals was estimated at about 6 hours but still heptachlor is subject to longrange transport and wet deposition.
The logarithmic soil organic carbon adsorption coefficient for heptachlor was estimated to be 4.38 which indicates a very high sorption tendency, suggesting that it will adsorb strongly to soil and is not likely to leach into groundwater in most cases. These properties suggest that heptachlor can remain deep in soil for years. The organic matter content of the soil is another factor affecting mobility. Heptachlor is less likely to leach from soil with high organic matter content. The halflife of heptachlor in temperate soil was reported to range between 6 months and 3.5 yrs. It has been found in studies that 16 years after the application of heptachlor, approximately 10% of the original amount was still present in the soil.
The log KOW for heptachlor suggests a high potential for bioaccumulation and biomagnification in the aquatic food chain.

 


Structure formula of Heptachlor


3D structure of Heptachlor