Textbook Problem

Products labeled as “organic” fill an increasing amount of space on supermarket shelves. What does that label mean? A food that carries the USDA’s organic label must be produced without pesticides such as malathion and chlorpyrifos that conventional farmers typically use on fruits, vegetables, and grains.

Does eating organic food significantly affect the level of pesticide residues in a child’s body? Chensheng Lu of Emory University used urine testing to find out. For 15 days, the urine of 23 children (ages 3–11) was monitored for breakdown products of pesticides. During the first 5 days (phase 1), children ate their standard, nonorganic diet. For the next 5 days (phase 2), they ate organic versions of the same types of foods and drinks. Then, for the final 5 days (phase 3), the children returned to their nonorganic diet. The results are shown in the Table.

Levels of Metabolites (Breakdown Products) of Malathion and Chlorpyrifos in the Urine of Children Taking Part in a Study of Effects of an Organic Diet*

		Malathion Metabolite		Chlorpyrifos Metabolite
Study Phase	No. of Samples	Mean (μg/L)	Maximum (μg/L)	Mean (μg/L)	Maximum (μg/L)
1. nonorganic	87	2.9	96.5	7.2	31.1
2. organic	116	0.3	7.4	1.7	17.1
3. nonorganic	156	4.4	263.1	5.8	25.3

* The difference in the mean level of metabolites in the organic and inorganic phases of the study was statistically significant

During which phase of the experiment was the maximum level of the chlorpyrifos metabolite detected?

Source: C. Lu et al. 2006. Organic diets significantly lower children’s dietary exposure to organophosphorus pesticides. Environmental Health Perspectives 114:260–263.