Sorption of trihalomethanes in foods
Trihalomethanes (THMs, namely, CHCl"3, CHCl"2Br, CHClBr"2 and CHBr"3) are disinfection by-products that are present in drinking water. These toxic chemicals are also present in meat, dairy products, vegetables, baked goods, beverages and other foods, although information regarding their concentrations and origin is very limited. This study investigates sorption of THMs occurring during rinsing and cooking of foods and the significance of food as an exposure source. Initial estimates of THM uptake were measured in experiments representing rinsing with tap water at 25C using nine types of food, and for cooking in tap water at 90C for fourteen other foods. A subset of foods was then selected for further study over a range of THM concentrations (23.7-118.7@mg/l), temperatures (25C and 90C), food concentrations (0.2-1.4, food weight: water weight), and contact times (5-240min). Data were analyzed using regression and exponential models, and diffusion models were used to help explain the trends of THM uptake. Among vegetables, sorbed THM concentrations at 25C were 213 to 774ng/g for CHCl"3, 53 to 609ng/g for CHCl"2Br, and 150-845ng/g for CHClBr"2. Meats at 90C tended to have higher concentrations, e.g., 870-2634ng/g for CHCl"3. Sorbed concentrations increased with contact time and THM concentration, and decreased with food concentration in rinsing tests (using spinach, iceberg-head lettuce and cauliflower) and cooking tests (using tomato, potato, beef and miso-tofu soup). For most foods, THM uptake was diffusion limited and several hours were needed to approach steady-state levels. Swelling, hydrolysis and other physical and chemical changes in the food can significantly affect sorption. Screening level estimates for CHCl"3 exposures, based on experimental results and typical food consumption patterns, show that uptake via foods can dominate that due to direct tap water consumption, suggesting the importance of sorption and the need for further evaluation of THM intake due to foods.