The dietary risk index system: a tool to track pesticide dietary risks

Background For years the United States Department of Agriculture’s Pesticide Data Program and the United Kingdom’s Food Standards Agency have published annual or quarterly data on pesticide residues in foods. Both programs report residues in conventionally grown, organic, and imported foods. The US program has tested about 288,000 food samples since 1992, primarily fruits and vegetables consumed by children. Since 1999 the UK has tested about 72,000 samples of a wider range of foods. These data are vital inputs in tracking trends in pesticide dietary risks. Methods The Dietary Risk Index (DRI) system facilitates detailed analyses of US and UK pesticide residue data, trends, and chronic risk distributions. The DRI value for a pesticide is the dietary intake of that pesticide from a single serving of food divided by the pesticide’s acceptable daily intake as set by the US Environmental Protection Agency. It can be calculated based on average annual residue concentrations, and on residue levels in individual samples of food. DRI values can be aggregated over multiple pesticides in single foods, and over individual pesticides in multiple foods. Results The DRI system provides insights into the levels, trends, and distribution of pesticide dietary risk across most widely consumed foods. By drawing on both US Pesticide Data Program and UK-Food Standards Agency residue data, the DRI is capable of assessing pesticide risks in a significant portion of the global food supply. Substantial reductions in pesticide dietary risks occurred in the early 2000s, primarily from replacement of organophosphate insecticides with seemingly lower-risk neonicotinoids. However, there remain several areas of concern and opportunities to reduce risks. Both herbicide and fungicide dietary risks are rising. Organically grown produce poses risks far lower than corresponding, conventionally grown produce. Risk differences are inconsistent between domestic and imported foods. Conclusions The surest ways to markedly reduce pesticide dietary risks are to shift relatively high-risk fruits and vegetables to organic production. For other foods, reducing reliance on pesticides overall, and especially high-risk pesticides, will incrementally lower risks. The DRI system can help focus such efforts and track progress in reducing pesticide dietary risk.


The USDA's Pesticide Data Program
In 2018, the USDA republished its entire PDP database, wherein nomenclature issues and inconsistent use of pesticide codes and names were standardized from 1992 to the present. This alleviated nearly all pesticide-nomenclature-related concerns arising from prior reports.
A remaining complication is that some parent compounds can also be a metabolite of another parent compound, e.g., omethoate is a metabolite of dimethoate, as well as a stand-alone active ingredient. In such cases, it is not possible to determine whether a residue of omethoate reported in a given food resulted from an application of an omethoate or dimethoate insecticide.
To address this problem as well as is possible, the DRI system generates its most detailed, food-pesticide-combination reports in two ways: (a) based on each pesticide's parent compound and any isomers or metabolites tested for and reported by the US-PDP, or (b) based on a pesticide-specific "risk group." Such a "risk group" aggregates all the analytes reported that can arise from an application of a specific active ingredient. The risk-group method assures that all relevant residues, and their associated DRI contributions, are included in a food-pesticide's DRI value.
For each analyte, the DRI value is calculated based on its reported residue levels and, where possible, its specific toxicity threshold. However, regulatory agencies usually assume that isomers and breakdown products are comparably toxic to the parent compound. Hence they use the same cRfD to quantify the contribution of isomers and metabolites to dietary exposures and risk. We do essentially the same in the DRI system.

The UK-FSA Pesticide Residue Testing System
The UK-FSA primarily tests foods for residues of parent chemicals. In 2012 it implemented a new nomenclature standard, in which "(sum)" or "(partial sum)" after the parent pesticide name signifies whether all, or only some, isomers or metabolites were Included.
In integrating UK-FSA residue data into the DRI system, we usually assume that all pesticide names followed by "(sum)" include the parent chemical and any of its known metabolites or isomers. Such residue levels are equivalent to US-PDP "total" residue levels.
There are a few exceptions to the assumption stated above. For some active ingredients for which the UK-FSA or US-PDP report "sum" or "total" residue amounts, it is not always clear what analytes are included. These uncertainties and our assumptions are noted in the following

Linking US-PDP and UK-FSA Residue Data
Linking UK-FSA pesticide active ingredient names with US-PDP names is straight forward, since the UK-FSA tests primarily for parent chemicals. Both systems have an assigned code from either the EPA or FSA. These codes are matched by pesticide name or by CAS numbers. Parent pesticides listed in the UK-FSA data set are linked to the parent pesticide or risk group used in the PDP data set. Pesticides in the UK-FSA system that are reported as partial sums will not link directly to the PDP system, since it is unclear which analytes are included in a partial sum.
The DRI system establishes a standardized name for each pesticide in both the US-PDP and UK-FSA systems that links it to other databases developed and maintained by Benbrook Consulting Services. These databases encompass a variety of activeingredient classifications and information: • EPA CAS and registration numbers; • Type of pesticide, chemistry family, and mode of action; • Post-harvest fungicide [Yes/No]; • Banned organochlorine [Yes/No]; • Registrant and regulatory history information; • Physical and chemical properties; • Toxicity data, safety factors, and regulatory thresholds (cRfDs, aRfDs, cPADs); • Pesticide use data in the US from the USDA; and • Oncogenic risk classifications and Q*s (if set).
For US-PDP pesticides no longer registered by the EPA, we use the most recent value of the active ingredient's cRfD or cPAD.
For pesticides tested by the UK-FSA but not by EPA, we use the cADI set by EFSA or other regulatory authority.
Some pesticides do not require dietary risk analysis by the EPA. Typically these are biopesticides that pose no, or very low, dietary risks because of low toxicity or absence of residues. Examples include insect pheromones, some microbial pesticides, horticultural oils, and mineral-based pesticides such as copper-based fungicides. For such products lacking an EPA-set cRfD or cPAD, we assign a default cRfD of 0.01 mg/kg body weight/day. This precautionary default value minimizes the chances of underestimating potential dietary risks if residues of these pesticides are reported in the future.

Serving Sizes Used in the DRI System
All DRI system outputs assume (1) a BW of 16 kg-the median for children near age 4 years, and (2) serving sizes nearly always equal to about 2/3 of FDA's RACCs for the general US population. RACCs were developed from national food consumption surveys and serve as guides for serving sizes listed on food labels (21 CFR 101.12 for most foods and 9 CFR 317.312 for some animal products) (1, 2). For a few US foods, we used available RACCs called NLEA serving sizes in USDA's National Nutrient Database for Standard Reference Legacy Release (SR Legacy), now at USDA's FoodData Central (3). NLEA refers to the Nutrition Labeling and Education Act of 1990 (4).
NLEA serving sizes were especially useful for lettuce types, because the best matching RACC for lettuce is for "vegetable salad" (100 g), whereas USDA lists NLEA serving sizes for 3 types of lettuce-89 g for crisphead lettuce and 85 g for Romaine and red leaf types. We used 87 g as a typical, average NLEA serving size for lettuce.
RACC and NLEA serving sizes are reported usually in metric weight (g) and volume measures (mL). To convert them to approximate US household units (e.g., tablespoons, cups and oz.), we used the weight-volume and weight-portion relationships in USDA's SR Legacy database. Table 1 shows some common and a few unusual examples of these conversions.
For most commodities tested by the US-PDP or UK-FSA, we used the following steps to determine serving sizes: look up the RACC or NLEA RACC serving size for that commodity, select a matching USDA food, select a USDA serving size with weight or volume near the RACC or NLEA serving size, record USDA's serving-weight relationship in both household units and g, and multiply by 2/3 to estimate the serving size for a 16-kg child. For lettuce which has multiple common forms, we used a composite of crisphead, Romaine, and red leaf types, and a composite of USDA's weight-volume relationships for these types. For rare foods with no RACC, we used a common commercial serving size (e.g., dry tea). The multiple versions of standard reports 2-8 can also include 3 market-claim options, denoted by the last letter of the report-naming matrix, as follows (see Table 3): A -All samples, regardless of market claim; C -Samples lacking a market claim, and referred to as "Conventionally Grown"; and O -Samples labeled as organically grown. For example, Report 3 food-pesticide DRI Values for samples of US domestically grown, conventional food tested by the US-PDP would be labeled: "Report 3_PDP_DC_DRI_by_Food." As detailed above, there are 12 residue data sets from which US-PDP DRI-system reports can be generated and 18 data sets for the UK-FSA DRI-system. Each residue data set includes a specific set of samples that match the selection criteria.
DRI output reports run from a few pages, to > 900 pages for the two most detailed reports (Reports 3 and 4). US-PDP Report 3_PDP_AA_DRI_by_Food, for example, reports DRI values by food, based on all samples from 1992 to 2018, and is 529 pages long, while Report 4__PDP_AA_DRI_by_Chemical reports DRI values for all foods and all samples in which a given pesticide or metabolite was found. It runs 1090 pages. For this reason,