Healthier Homes and Gardens
February 2008

Children's exposure to pesticides has been documented in several "snapshot" studies that tested for a range of pesticide residues in single urine or blood samples. Using a novel approach, a recent study of Seattle area children tested two daily urine samples over a period of days looking for residues of two types of insecticides — organophosphates and pyrethroids. By alternating children's diet between conventionally and organically grown food, researchers were able to see a bigger picture that pointed toward food or other factors as the source of their exposure.

Results reported so far boiled down to this: Organophosphate insecticides were not used by any families in their homes, but the children were still exposed through their food except when they switched to organic produce. In the case of pyrethroids, children continued to be exposed, even when organic produce was substituted. Children whose families used pyrethroid insecticides in and around the home had the highest levels of pyrethroids and analysis showed that this home pesticide use was their primary source of exposure.

The Study

To learn more about the contribution of diet and residential pesticide use to children's pesticide exposure, researchers did a longitudinal study of 23 children ages 3 to 11 from the Seattle urban and suburban area. The children's families normally ate only conventionally grown food. During four seasonal study periods parents collected their child's urine twice a day and also kept food logs. The urine was tested for indicators (called metabolites) of both organophosphate and pyrethroid insecticides. Parents also reported on pesticides that were used in and around the home.

In the summer of 2003, researchers substituted organic food items for five of the fifteen day study period. Organic food samples were tested to confirm that they were free of any pesticide residues. In 2006, analyses of both organophosphate and pyrethroid data from this first study phase were published in two articles in the journal Environmental Health Perspectives.

The study continued with three more testing periods during the following fall, winter and spring. The report on organophosphates over this extended period was published online in January 2008 on the Environmental Health Perspectives web site.

Organophosphates

The first phase of the study clearly showed that children were exposed to organophosphates through their diet. All parents reported that they had not used organophosphate products in and around their home. However organophosphates were detected in children's urine throughout the study period. This changed dramatically during the five days when organic food items were substituted for matching items that they normally ate.

Focusing on two chemicals, chlorpyrifos and malathion, testing showed that median concentrations of the chemical indicators decreased to nondetectable levels within the 5 days. Reintroduction of conventional food items — primarily fruits and vegetables — brought pesticide residues back up to previous levels. The authors stated that "an organic diet provides a dramatic and immediate protective effect against exposures to organophosphate pesticides..."

Studies done during fall, winter and spring brought new insights. Organic food substitution in the fall study confirmed that food was the source of children's exposure. Looking at all four seasons, researchers concluded that eating fresh produce year round affected the residue levels of chlorpyrifos and malathion. Researchers suspected that imported food eaten during winter and spring might have been a contributing factor. Compared to domestically grown food, evidence from other sources shows that these two chemicals contaminate certain imported items more frequently and at higher levels.

By 2000, the Environmental Protection Agency had begun restricting uses of organophosphates because of their ability to harm the nervous system. At the time of this study, chlorpyrifos was already banned from use in homes and schools. Malathion products were (and still are) available for gardeners. These two chemicals and other organophosphates continue to be widely used in agriculture.

Pyrethroids

During the same 2003 summer study period described above, researchers also tested for indicators of pyrethroid insecticides that became more widely used in both urban and agricultural settings after some restrictions on organophosphates were implemented.

In the case of pyrethroids, eating organic foods instead of conventional foods did not produce any dramatic effects. Researchers detected pyrethroids throughout the study and many urine samples continued to show pyrethroid contamination during the organic period without indicating a downward trend.

However, differences came out when the seven children whose families reported using pyrethroid products in or around the home were compared to the other 16 children. Some of these seven children had the highest levels of some pyrethroid indicators. In the most extreme case, the parents had sprayed furniture, including beds. All seven children were exposed continuously during the 15 day study indicating that residues from home treatments were still present in the environment.

While analysis showed that children's exposure to pyrethroids was partially attributable to residues on food, use of home use of pesticides was the primary source of exposure. The parents reported using products that contained pyrethroids such as permethrin, deltamethrin and pyrethrins and were used for both garden pests or indoor pests such as fleas and carpenter ants.

Researchers were somewhat surprised to find that older children (8-11 years) in the study had higher levels of pyrethroids than younger children (3-7 years). Other studies have suggested that younger children are more exposed to pesticides, likely due to hand-to-mouth behavior and playing on the floor. In the Seattle study, families reported that older children were more involved in sports and other activities away from home than younger children. Researchers speculated that the older children may have been exposed to pyrethroid products used in recreation sites.

The researchers concluded that children's exposure to pyrethroid insecticides could be reduced by minimizing the use of these products around the home or preventing children from coming into contact with areas or objects that had been treated with these pesticides.

Corrected version posted March 6, 2008.

REFERENCES

Lu, C. et al. 2006.
Organic diets significantly lower children's dietary exposure to organophosphorus pesticides.
Environmental Health Perspectives 114(2):260-263.
abstract: http://www.ehponline.org/docs/2005/8418/abstract.html
article: http://www.ehponline.org/members/2005/8418/8418.pdf

Lu, C. et al. 2006.
A longitudinal approach to assessing urban and suburban children's exposure to pyrethroid pesticides.
Environmental Health Perspectives 114(9):1419-1423.
abstract: http://www.ehponline.org/docs/2006/9043/abstract.html
article: http://www.ehponline.org/members/2006/9043/9043.pdf

Lu, C. et al. 2008.
Dietary intake and its contribution to longitudinal organophosphorus pesticide exposure in urban/suburban children.
Published online January 15, 2008: doi:10.1289/ehp.10912
article: http://www.ehponline.org/members/2008/10912/10912.pdf

NEWS STORY

Andrew Schneider. Seattle Post-Intelligencer. January 30, 2008.
Harmful pesticides found in everyday food products: Mercer Island children tested in yearlong study.
http://seattlepi.nwsource.com/local/349263_pesticide30.html