About the Data

About DDE and DDT in breast milk:

DDT is an organochlorine once widely used as a general insecticide, a compound that is still present in the environment. DDE is a product of biological degradation of DDT. Both DDT and DDE are lipidphilic ("fat loving") and therefore are concentrated in the breast milk of mammals, including humans. The presence of DDT in breast milk represents recent intake of this chemical, while the presence of DDE reflects longer term exposure. If a nursing mother has consumed a large quantity of DDT during her life, she may pass this insecticide and its byproduct onto her infant. Infants are typically far more susceptible to neurological and developmental damage from toxic chemicals than adults.

The Yakima River Valley in central Washington State is one of the most productive agricultural areas on Planet Earth. Large quantities of pesticides, including DDT, have been used in this region. As a consequence, many organisms such as bottom-feeding fish in the Yakima River have very high concentrations of DDT and DDE; DDT is magnified up the food chain and represents a classic example of bio-amplification. High order consumers such as humans are therefore at risk for ingesting and accumulating large quantities of DDT and DDE.

Marien (1998) has examined fish consumption among Hispanics in the Yakima Valley, to assess the impact of diet on breast milk and infant exposure to DDT and DDE. Twelve individuals in three different groups were sampled for comparison; a dozen Mexican Hispanics consuming at least one DDT-contaminated fish meal per week (referred to as "exposed" individuals), a dozen US-born unexposed people (non fish-eaters), and a dozen Mexico-born unexposed individuals. A sample size of 12 is quite small, and therefore the uncertainty of the results will be much greater than in a study with larger samples. However, increasing the sample size tends to increase the number of extraneous variables, especially in a complex organism such as a human being. To help mitigate some of this variability, each exposed individual was matched to two unexposed individuals with the same number of breast-fed children and the same duration of breast-feeding.

The study results show a wide range of values of both DDE and DDT in the milk of Yakima Valley Hispanics, regardless of which group is considered. Why would people within a single group show such a wide range of contamination? Students should think of several fundamentally different reasons for the varying levels of DDE and DDT concentration.

Are there differences between the 3 different populations? The students can approach this question a number of ways, using mean, median, min and max. What might be the cause of these differences between groups? Are the differences statistically significant? Advanced students can use various tests, such as ANOVA.

What about the effect of fish consumption on DDT and DDE concentration? Why did the unexposed Mexico-born Hispanics have higher concentrations than the exposed Mexico-born Hispanics?

Sources:

Marien, K (1998), DDT and DDE transmission through breast milk: Yakima River Basin; Report to the Washington State Dept. of Health, Office of Environmental Health Assessment Services.

Marien K, Conseur A and Sanderson M (1998), The effect of fish consumption on DDT and DDE levels in breast milk among Hispanic immigrants; J. Human Lactation, vol 14, # 3, pp. 237-242.

Many thanks to Koenraad Marien for providing the original data.