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DBCP In Drinking Water: What Does It Mean? Page 3 department or water testing laboratories. The current average cost of laboratory analysis is about $90). Extensive testing of wells has already been conducted in high DBCP use areas, and about 1,500 public and private wells have been voluntarily removed from services because they exceeded the earlier, nonenforceable guideline (Action Level) of 1 ppb. WHAT ARE THE HEALTH EFFECTS OF DBCP? The two health hazards of concern for DBCP are cancer and male infertility. CANCER Laboratory experiments have shown that mice and rats fed DBCP developed cancer. When a chemical causes cancer in two species of test animals, scientists consider it likely to cause cancer in humans. Several studies of human cancer and DBCP have been conducted without clear results. A preliminary study by the California Department of Health Service in 1982 found that cancer deaths were higher in areas where DBCP concentrations in the drinking water were higher. Specifically, it found a statistical relationship between increasing DBCP concentration in drinking water and stomach cancer and leukemia in persons consuming the water. This study only used data from death certificates and did not take into account important complicating factors such as ethnic backgrounds, which could influence dietary intake. Four other studies involving humans have not confirmed increased cancer incidence. Two studies reported in 1986 did not find a statistically significant relationship between DBCP in drinking water and increased cancer. Two other studies have examined cancer in workers who were exposed to DBCP and found no cancer increase. All of these studies, however, have been inconclusive because of problems such as low levels of DBCP exposure, small study populations, or short follow-up time. Follow-up time is important because it may take 20 years or more for cancer to show up after exposure has occurred. Therefore the human studies so far have not told us whether or not DBCP causes cancer in humans. Because of the problems with human studies, DHS scientists used data from the animal experiments to estimate DBCP's cancer potency and the risk it represents to humans in drinking water. This formed the health basis of the MCL for DBCP. Animal studies are routinely used for such purposes because they can be conducted under carefully controlled conditions. Also, most chemicals that cause human cancers also cause cancer in animals. The animal studies for DBCP also have some flaws, but they were considered adequate for assessing cancer risk.