Organochlorine pesticide residues in breastmilk: difficulties in sample collection and in assessing intakes

Organochlorine pesticides are highly lipophilic and stable resulting both in their persistence in the environment and their tendency to pass up the food chain. Residues of these compounds are detectable in breastmilk and have been monitored since the 1950s. Samples can be collected using non-invasive techniques and the results are frequently used to assess degradation in the environment as well as risks to recipient infants. As a food, breastmilk is unique. It is manufactured entirely for an individual consumer with some of its constituents driven by its recipient. It can form the sole source of nutrition for a considerable period of an infant's life. Standard calculations of exposure to residues rely on consumption of 750–850ml breastmilk day-1 containing 3.5% fat for a 5-kg infant. The fat content of breastmilk, however, is highly variable, which means that that using fixed breastmilk volumes and fat can lead to an imprecise calculation of individual risk. The fat concentration of breastmilk changes throughout a single feed, between feeds and as lactation progresses. This variation therefore raises the methodological problem of how to secure a representative sample of breastmilk. Furthermore, maternal factors such as age and parity also affect concentrations because of the persistence of organochlorine pesticide residues in maternal fat stores. It is therefore critical that samples are collected in a systematic manner taking account of these variables, particularly if the results not only are to be used for risk assessment, but also in comparing changes in environmental concentrations. Reviews of the literature have shown that these variables have often been disregarded in drawing up sampling strategies and methodologies are poorly reported in publications. The paper discusses the literature currently available on monitoring organochlorine pesticide residues in breastmilk and presents an overview of some of the factors that need to be taken into account when collecting samples and assessing infant exposure.