Volume No. 3 Issue No.: 3 Page No.: 893-921 Jan-Mar 2009




Rabi Narayan Sharma, Bandana Mahto and Sudha Goel*

Civil Engineering Department (Environmental Engineering and Management) Indian Institute of Technology Kharagpur, Kharagpur, West Bengal, (INDIA)


Received on : October 01, 2008




All drinking water sources contain natural organic matter (NOM) and addition of chlorine to drinking water results in the formation of various chlorinated disinfection by-products (DBPs). Some of these DBPs are carcinogenic and are regulated in most developed countries. This paper is a review of the current levels of understanding about DBP toxicity and the magnitude of risk due to exposure to DBPs. Various routes of exposure have now been examined and the latest findings prove that ingestion of chlorinated drinking water is no longer the major route of exposure. THM levels in blood were far higher after exposure to chlorinated drinking water via dermal absorption and inhalation during showering, bathing or swimming. Evidence of DBP toxicity comes mainly from animal toxicity studies and to a smaller extent from epidemiological studies. Two common methods of studying toxicity are by feeding the chemical of concern to animals (generally rodents) via drinking water or gavage (force-feeding). More gavage studies were found to show carcinogenic effects in comparison to oral toxicity studies. However, the effect of route of exposure, i.e., oral versus gavage, has not been examined systematically in any animal toxicity study and is likely to be a confounding factor. The site of tumor formation in most animal toxicity studies were liver, kidneys, intestines and thyroid. Most epidemiological studies found in the literature were conducted in developed countries and excess risk was found for bladder, rectal and colon cancer. Also, exposure to chlorinated surface waters was found to result in greater risk of cancer compared to chlorinated groundwater. This may be attributed to higher levels of DBP formation in surface waters and other sources of contamination in surface waters. Reproductive effects were also examined in both types of studies; no or little association was found between exposure to chlorinated water and increased risk of miscarriages, low birth weight, or preterm delivery. All three outcomes were found to decrease with increase in amount of water ingested.


Keywords : Disinfection by products, Carcinogenic effects, Organic matter, Microbial pathogens.