Formation of trichloromethane in chlorinated water and fresh-cut produce and as a result of reacting with citric acid

Authors: Fan, Xuetong; Sokorai, Kimberly

Submitted to: Postharvest Biology and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/11/2015
Publication Date: 6/11/2015
Publication URL: http://handle.nal.usda.gov/10113/60995
Citation: Fan, X., Sokorai, K.J. 2015. Formation of trichloromethane in chlorinated water and fresh-cut produce and as a result of reacting with citric acid. Postharvest Biology and Technology. 109:65-72.

Interpretive Summary: Chlorine (sodium hypochlorite) is commonly used by the produce industry to sanitize wash water, fresh fruits and vegetables. However, possible formation of harmful chlorine by-products is a concern. In the present study, we evaluated the formation of trichloromethane (a major chlorine by-product) in chlorinated wash water and cut vegetables. Result showed that low levels of trichloromethane were formed in wash water and cut lettuce. Importantly, citric acid, a chemical often used to adjust pH of chlorine solution, is the major factor contributing to trichloromethane formation. Therefore, to reduce the formation of harmful chlorine by-products, citric acid should be replaced with other pH adjustors. The information will help produce industry and regulatory agencies to minimize safety hazard in our food supply.

Technical Abstract: Chlorine (sodium hypochlorite) is commonly used by the fresh produce industry to sanitize wash water, fresh and fresh-cut fruits and vegetables. However, possible formation of harmful chlorine by-products is a concern. The objectives of this study were to compare chlorine and chlorine dioxide in trichloromethane formation, determine trichloromethane levels in chlorinated wash water, cut-lettuce and diced onions, and evaluate the reaction of chlorine with citric acid, a chemical often used to adjust pH of chlorine solution. Results showed that trichloromethane levels increased from 0 to 40 g/L as chlorine concentration increased from 0 to 200 mg/L when the chlorine solutions were mixed with lettuce extract. Little trichloromethane (less than 3g/L) was produced from chlorine dioxide solution even at concentrations up to 200 mg/L. The formation of trichloromethane in 1 L of 100 mg/L chlorine wash water increased from 155 to 284 g/L after repeated use of the wash water to wash six batches of 100 g cut lettuce. Levels of trichloromethane in the washed cut lettuce were in the range of 14-22 g/g, and were reduced to less than 8 g/g after being rinsed with water. Chlorine solution used to wash diced onions produced much less trichloromethane (32 g/L) compared with that for washing cut lettuce despite higher chemical oxygen demand and turbidity in the wash water. Citric acid reacted with chlorine and produced trichloromethane. Over 1,000 g/L trichloromethane was produced after 30 min reaction with chlorine at 22C, while less than 35 g/L trichloromethane was produced when Na-phosphate was used to adjust pH of chlorine. The amount of trichloromethane increased with reaction time and concentration of citrate. Our results demonstrated that formation of trichloromethane in wash water depended on type of cut-vegetables. Furthermore, citric acid contributed to a significant amount of trichloromethane formation.