Drinking Water Contaminants- Dichloromethane (DCM)

　　This document delves into a chemical that may be found in both public and private drinking water systems and could cause health concerns when levels surpass the health-based benchmarks set by the EPA. What Is Dichloromethane and What Are Its Applications? Dichloromethane (DCM), akin to chloroform, is a colorless, sweet-scented organic liquid predominantly used as a paint remover. Additionally, it serves as a solvent and cleaner across various sectors, as a fumigant for produce and grains, and in the extraction of substances from food.

　　Alternative Designations and Synonyms: DCM, Methylene chloride

　　The Regulatory Justification for DCM: The Safe Drinking Water Act of 1974 directs the EPA to establish safe thresholds for contaminants in drinking water that may be detrimental to health. The Maximum Contaminant Level Goal (MCLG) for DCM is zero to forestall health risks. As such, the EPA has determined a Maximum Contaminant Level (MCL) of 5 parts per billion (ppb) as the enforceable standard for water systems.

　　Health Concerns: Exposure to DCM above the MCL in the short term may harm the nervous system and blood. Chronic exposure may lead to liver damage and an increased risk of cancer.

　　Environmental Discharge of DCM: The production of DCM decreased from 561 million pounds in 1986 to around 410 million pounds in 1993. It is largely discharged into wastewater from industries such as paint and ink production, aluminum manufacturing, coal mining, among others, and is also produced during water chlorination. From 1987 to 1993, over 2.1 million pounds of DCM were released into terrestrial and aquatic environments, with the highest emissions occurring in Connecticut and New York.

　　Environmental Disposition of DCM: DCM predominantly enters the atmosphere where it is photolyzed within a few months. In aquatic environments, it evaporates swiftly. While it can permeate soil to reach groundwater, it is not likely to bioaccumulate in aquatic organisms.

　　Detection and Elimination of DCM: Since 1994, the EPA has mandated water suppliers to test for DCM levels above 0.5 ppb and to employ removal techniques like Granular Activated Carbon and Packed Tower Aeration when levels exceed the MCL.

　　Public Notification: If DCM levels exceed the 5 ppb MCL, water suppliers are required to notify the public through various media outlets and may need to supply alternative water sources to reduce health risks.

　　Drinking Water Quality Standards:

• MCLG: 0
• MCL: 5 ppb

　　DCM Emissions to Water and Land, 1987-1993 (in pounds):

• Water: 1,544,694
• Land: 556,830

　　The aforementioned totals and the key industries contributing to DCM emissions are part of the EPA’s National Primary Drinking Water Regulations, which are designed to protect public health through the enforcement of drinking water quality standards.