1,2-Dibromo-3-chloropropane (DBCP)

DBCP was developed in the 1950s as a highly effective nematicide — it kills the microscopic roundworms (nematodes) that damage the roots of fruit trees, grapes, and other crops [1]. It was widely used in California's San Joaquin Valley, Hawaii (on pineapples), and throughout tropical fruit-growing regions worldwide from the 1950s through the 1970s. The first hint of its reproductive toxicity came in 1977 when workers at an Occidental Chemical plant in Lathrop, California noticed that few of them were having children, and several voluntarily submitted to sperm testing — finding dramatically reduced or absent sperm counts [2]. Investigation revealed that virtually all male workers at the plant who had significant DBCP exposure were sterile or severely infertile. This led to emergency EPA regulatory action in 1979, when most DBCP uses were cancelled. But decades of soil application had left enormous DBCP residues in the deep aquifers of the San Joaquin Valley, where it remains detectable in hundreds of community water systems to this day [3].

Historical agricultural worker exposure was through skin absorption and inhalation during application and handling — DBCP is readily absorbed through all routes [1]. Today, community exposure is primarily through contaminated drinking water from Central Valley aquifers. DBCP is particularly persistent in groundwater because the deep sandy aquifers of the San Joaquin Valley act as reservoirs — the compound does not easily degrade in anaerobic conditions. Over 100 community water systems in California have detected DBCP above health guidelines [2]. People on private wells in the central San Joaquin Valley face the highest ongoing exposure risk. Workers in the few remaining countries where DBCP use continues (it was not banned in many tropical countries until the 1990s or later) face ongoing occupational exposures [3].

DBCP is one of the clearest examples of an occupational reproductive toxin: it is specifically toxic to spermatogenic stem cells in the testis, causing the depletion of sperm-producing cells and resulting in oligospermia (reduced sperm) to azoospermia (no sperm) [1]. Recovery of fertility after cessation of exposure occurred in some men but not all — those with the most severe cell depletion had permanent sterilization. DBCP is also classified as a probable human carcinogen, with animal evidence for stomach, kidney, adrenal, and liver tumors [2]. Female reproductive toxicity is also documented. The drinking water concern is significant because DBCP is both a carcinogen and a reproductive toxin in a population with no choice about their water source [3].

Residents of the San Joaquin Valley who rely on private wells or small water systems without DBCP treatment face the most significant ongoing US exposures [1]. Male agricultural workers who were employed in DBCP application in the 1960s–1970s who experienced infertility should discuss DBCP history with their physician — cancer surveillance may be appropriate [2]. People in tropical countries where DBCP was used more recently on bananas and pineapples into the 1980s and 1990s also have elevated exposure histories.

San Joaquin Valley residents should test their private well water for DBCP — even if the well was tested years ago, DBCP plumes can migrate [1]. If detected above California's 0.2 ppb action level, use reverse osmosis or activated carbon block filtration for drinking and cooking water. Connect to municipal water if available [2]. Advocate for California's Water Board to monitor and address DBCP-contaminated water systems — many small rural water systems lack the resources to install treatment [3]. Male workers with significant historical DBCP exposure and fertility concerns should consult a reproductive urologist.