Short and Long Term Fate of Environmental Pollutants and Their Management

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There has been an increasing demand of chemical substances during this and the last century. The use of chemicals for a long time has been identified as a negative impact on the environment since it became apparent that residues could be transferred through the food chain; remain in soil or sediment as intractable substances. Chlorinated pesticides stand as a classic case of intractable substances and their residues remain dispersed throughout the world. Even though banned, their use continued because of their effectiveness as insecticides and availability. The effective use of DDT (dichlorodiphenyltrichloroethane) for control against malaria was recognized following its removal but was reinstated for controlled situations. Arsenic is another classic case because its residues from the application of its compounds as insecticides for cattle dips remain as buried residues that are intractable. The soil from such repositories requires remediation. The recognition of problems associated with the lifetime of long persistence substances led to the need to use low persistent pesticides for insect control. The impact of increasing use of pesticides and herbicides is now offset by available data which shows that for many compounds, residues are undetectable in soil and groundwater. The USGS found no significant build-up of low persistence pesticides in groundwater over a 15 years period. Long-persistence or intractable compounds require specific techniques of soil remediation to deal with their effects on plants and animals. Examples of substances that may require soil remediation are arsenic, dioxins and DDT. A classic case of dioxin in soil was spotted at Bien Hoa, Vietnam, where 1 ppm TCDD (2,3,7,8-Tetrachlorodibenzo-p-dioxin) was found in soil. A remediation plan was put in place and the TCDD residues were excavated and disposed in a repository. While exceptions occur, it is important to recognise that degradable chemicals should be used wherever possible in order to avoid future remediation problems.