A number of factors must be taken into account in order to produce the most accurate and reliable set of DRIs, and to properly apply the DRI in tracking changes in pesticide risk levels and distribution over time. Some impact the exposure side of the DRI equation and limits inherent in the PDP dataset, while others reflect issues involving pesticide toxicity and how cRfCs are calculated.
Dealing with Isomers and Metabolites
The PDP tests foods for parent pesticide active ingredients, as well as major metabolites and/or isomers. In many cases, the PDP has changed how it reports the residues of a particular pesticide over time. In general, PDP has added more metabolites and isomers in recent years, in an effort to more completely account for possible residues stemming from a given application of an active ingredient
In a small number of cases, the PDP has reported in some years, but not all, results for “Total” or multiple residues (e.g., “Total Endosulfans” and “Endosulfans,” or “Total Permethrins” or “Permethrins”), in addition to the parent compound and one to several metabolites/isomers combined. In such cases, special care must be exercised to avoid double counting residues and risk in estimating DRIs
In cases where the PDP reports results for individual isomers and metabolites, as well as “total” residues of the pesticide, DRI values for such a pesticide are based just on the “total” residue results. This is necessary to avoid possible double counting of residues present in a given food.
When PDP reports values for the parent compound and one or more isomer or metabolite, a DRI value is calculated for each based on the residue data specific to the parent compound, isomers, and metabolites, and then added together to equal the total pesticide DRI. In most cases, EPA does not request nor evaluate toxicology data on metabolites and isomers, and for this reason calculates risks associated with exposures to metabolites and isomers using the cRfD or cPAD associated with the parent chemical. This same approach is used in estimating DRI values.
Residues Not Linked to Field Applications
Some of the pesticide residues detected in a given food in the course of PDP testing may not stem from applications of pesticides in the field during the growing season. For many fruits and vegetables, one-third to one-half of the residues found are from fungicides applied post-harvest, typically in storage facilities. Clearly, farmers have no control over these applications
Chlorinated hydrocarbon insecticides (e.g., DDT, aldrin, toxaphene, chlordane) that were banned some 30 years ago still account for the majority of residues found in many animal products and some root and leafy green crops. Again, there is little a farmer can do to avoid these residues when crops are grown that are prone to taking up soil-bound organochlorine residues
A significant share of the residues found in organic food samples are from drift, contaminated fog or water, or residues bound in the soil (Baker et al., 2000). Growers have little or no control over these classes of residues.
Baker, B. P., Benbrook, C. M., Groth, E., and K.L. Benbrook. “Pesticide residues in conventional, integrated pest management (IPM)-grown and organic foods: insights from three US data sets.” Food Addit.Contam 19.5 (2002): 427-46.