Correlation Between Pesticides and Reduced Male Fertility
(Beyond Pesticides, January 19, 2006) A study published in the January issue of Epidemiology has found inverse associations between pesticides and male testosterone levels. The study, conducted by researchers at University of Michigan, Harvard University, and the Centers for Disease Control and Prevention in Atlanta, has found that high levels of the urinary metabolites of chlorpyrifos (TCPY) and carbaryl and naphthalene (1N) correlate directly with low levels of testosterone in male subjects.
The researchers studied urine samples from 268 male clients of a Massachusetts fertility clinic between 2000 and 2003. The results of the study found an inverse correlation between high levels of the urinary metabolites and low levels of testosterone. The researchers feel that the study is environmentally relevant since the levels of TCPY and 1N found in the subjects is consistent with the results of national studies looking at human pesticide exposure.
Environmental exposure to these chemicals is not a new discovery. According to the researchers, “The Second National Report on Human Exposure to Environmental Chemicals (carried out within NHANES 1999-2000) found that more than 90% of males in the U.S. population had urine samples with detectable levels of TCPY…The Report also found that over 75% of U.S. males have detectable levels of 1N.” Although residential use of chlorpyrifos, a broad-spectrum organophosphate, was highly restricted in 2000, high rates of TCPY are still being found in urine. Exposure is most likely continuing due to the environmental persistence of the pesticide. Although chlorpyrifos is commonly referred to as “nonpersistent”, it can persist for an extended period of time if in the right conditions. Trace amounts of chlorpryifos continue to be found in many different foods, also providing a common exposure route.
The researchers believe that the correlation between the pesticides and reduced male fertility may be due to the enzyme disruption associate with the chemicals. Chlorpyrifos is a known cholinesterase inhibitor, which the researchers believe may affect the release of luteinizing hormone (LH), the hormone that triggers testosterone secretion from the Leydig cells.