University of Washington’s Cynthia Curl and her fellow authors surveyed nearly 4,500 people about what they eat. They combined this information with average residue levels in those items from the U.S. Department of Agriculture’s Pesticide Data Program to estimate their intake of organophosphate pesticides (OPs). Organophosphates are a group of manufactured chemicals that are the most widely used insecticides today but are not allowed for use in organic farming.

Symptoms of sudden poisoning by organophosphates include headache, dizziness, weakness, diarrhea, nausea and vomiting, salivation, watery eyes and small pupils. Severe symptoms include seizures, slow pulse, difficulty breathing and coma.

Long-term exposure to organophosphates can cause confusion, anxiety, loss of memory, loss of appetite, disorientation, depression and personality changes. After exposure, people can also develop nervous system problems such as muscle weakness and numbness and tingling of the hands and feet, and some studies in adults and children have linked organophosphate exposure to lymphoma and leukemia.

In their study, Curl and her team also collected urine samples from 720 people to test for dialkylphosphate (DAP) metabolites — common byproducts of the body metabolizing most OPs. DAP concentrations supported the estimated pesticide exposure, and the researchers also found that the 240 participants who said they ate more organic produce had “significantly lower” DAP concentrations.

This isn’t the first study relating to chemical residues and food consumption, but it is the first to include information on organic food consumption habits. “The food composition — chemical residue method described in the present study may prove useful in future epidemiological studies of long-term dietary OP exposure, particularly if paired with information on organic food consumption, which may modify the observed exposure-response relationship,” the authors wrote. “As concern grows regarding potential effects of low-level OP exposures, the need increases for more sophisticated exposure assessment methods.”