It’s no secret that these pesticides can harm the nervous system. Organophosphate pesticides block an enzyme, acetylcholinesterase, that is critical for proper transmission of signals from one nerve to the next. Shortly after being exposed to a high dose of organophosphates, a person will suffer weakness, cramps, breathing trouble, nausea, and vomiting (USEPA 1999). Worse, some effects may persist long after exposure. In one study, farm and pest-control workers tested months to years after a pesticide-poisoning incident had poorer memory and damaged motor skills, as well as anxiety, depression, and confusion (Eskenazi 1999). Carbaryl has similar immediate effects on the nervous system. Inhaling or ingesting large amounts can cause nausea, stomach cramps, and diarrhea, as well as sweating, blurred vision, loss of coordination, and convulsions (USEPA 2003).

Increasing evidence from animal studies also indicates that the brain development of fetuses and children may be impaired by exposure to organophosphates. Studies in young mice found that a single dose of an organophosphate caused permanent damage to brain function, including hyperactivity (Ahlbom 1995). Similarly, mice with prenatal exposure to diazinon had poorer coordination and endurance, as well as delayed sexual development (Schettler 2000). Rats with prenatal exposure to chlorpyrifos had smaller brain weights and decreased reflexes (Chanda 1996, Schettler 2000).

Recent studies in farmworker populations indicate that developmental damage from these pesticides is occurring in people. University of California researchers have studied a group of children born to farmworkers in California’s Salinas Valley, where 500,000 pounds of organophosphate pesticides are used each year. In a 2005 study, the group reported that infants with greater exposure to organophosphates had more abnormal reflexes (Young 2005). They also found that mothers with higher exposures are at increased risk for preterm birth (Eskenazi 2004). In Oregon, researchers compared neurological performance of farmworkers with that of an immigrant community living on the coast and with little exposure to pesticides (Rothlein 2006). Their findings: adults with greater exposures to organophosphates scored more poorly in tests of attention spans and motor function.

There’s also powerful evidence that carbaryl may cause cancer; EPA considers carbaryl a likely human carcinogen (USEPA 2003). Several studies have reported greater incidence of childhood brain cancer in homes using carbaryl (Davis 1993) or types of products that may contain carbaryl (Pagoda 1997). Other studies have found an elevated risk of non-Hodgkins lymphoma (NHL) among farmers who handled carbamate insecticides in general and carbaryl in particular. A study of Canadian farmers showed that those using carbaryl had twice the incidence of NHL (McDuffie 2001). A reanalysis of pooled data from three separate studies in several Midwestern states found a 60% increase in NHL among farmers who reported using carbaryl (Zheng 2001). While these studies don’t prove an association, their sample sizes were large and their findings correlate with evidence from animal studies linking carbaryl to immune suppression, a known risk factor for NHL.