DRI Technical Details

Data Sources

The DRI system integrates and draws upon three primary sources of data:

  • Annual residue data from the US-PDP and UK-FSA pesticide residue testing programs,
  • Chronic toxicity data on pesticide active ingredients, metabolites, and isomers from the US EPA or the European Food Standards Agency (EFSA), and
  • Food categories and serving sizes from the U.S. Department of Agriculture.

Residue Data

Annual US-PDP data files have been downloaded and incorporated into the DRI system.

Via hard-copy reports beginning in 1999, the UK-FSA reported sample-specific residue data quarterly. We moved sample identifiers and results data from these UK-FSA reports into the DRI system. The UK-FSA began providing these data in digital spreadsheet form in 2016.

To make the quarterly UK-FSA data compatible with annual US-PDP data, quarterly UK-FSA report results were combined by calendar year.

Because some crops are stored and marketed in a subsequent year, there is not a perfect match between the US-PDP and UK-FSA data sets regarding the year a crop was grown and the year it was tested for pesticide residues.

Budget constraints limit the number of foods the US-PDP and UK-FSA can test in any given year, creating gaps between the years when a given food was tested.

Technical sophistication in both programs has steadily improved, as has the number of foods, food forms, and pesticide analytes tested (“analytes” include parent compounds, metabolites, and isomers).

Limits of detection (LODs) and limits of quantitation (LOQs) have trended downward in both programs over the last 30 years.

Various methods have been used inconsistently in the US-PDP and UK-FSA to quantify and distinguish between residues of parent-active ingredients, various metabolites, and related moieties. This creates challenges in tracking changes in DRI risk levels over time.

The DRI system resolves pesticide name, metabolite, and moiety differences within the US-PDP and UK-FSA data sets. The system deals with pesticide naming differences by linking all analytes arising from the use of an active ingredient to a common, parent-pesticide name.

The UK-FSA’s program casts a wide net across the UK food supply, testing 40 to 60 foods annually. The program places heavy focus on residue levels and trends in the approximately 80% of the UK food supply that is imported. It usually tests just a few to 150 samples per food or food form per quarter.

The US-PDP focuses predominantly on foods making up a significant share of the diets of pregnant women, infants, and children, and tests 15 to 25 foods and food forms annually.

It usually tests 300 to 700 samples per food in each, annual program cycle.

The ability to draw on both US-PDP and UK-FSA residue data in the DRI system allows, for the first time, comprehensive assessments of pesticide dietary-risk levels and trends across foods and pesticides in a significant share of the global food supply.

The opportunity to identify low-risk and high-risk food-pesticide combinations has important ramifications for targeting regulatory interventions and guiding efforts by farmers and the food industry to incrementally lower overall pesticide dietary risks.

Pesticide Toxicity Data

All DRI values are based on current US EPA or EFSA estimates of a pesticide’s chronic toxicity.

The US EPA calculates pesticide-specific chronic Reference Doses (cRfDs). All cRfDs are derived from the adverse health effect observed in animal studies at the lowest no-effect level. We explain much more about how these values are set and applied in our Pesticide Risk Assessment and Regulation section.

The “no-effect level” is the next lower dose level in an animal study, below the lowest level where an adverse health impact was observed.

A pesticide’s cRfD is typically calculated by dividing the lowest “no effect level” from animal studies by a standard, 100-fold safety factor.

When the added, 10-fold safety factor called for by the 1996 FQPA is invoked, a pesticide’s cRfD becomes a chronic Population-Adjusted Dose (cPAD).

Some pesticides detected by the UK-FSA are not regulated by the US EPA, and hence lack EPA-set cRfDs or cPADs needed to calculate DRI values. In such cases, the DRI system uses chronic Acceptable Daily Intake (cADIs) thresholds set by the European Food Safety standards (EFSA).

Biopesticides thought by regulators to pose no meaningful dietary risk are not subject to chronic toxicology testing requirements, and hence there is no basis to set cRfDs, cPADs, or cADIs. In such cases, the DRI system assigns a conservative default cRfD of 0.01 mg/kg/day.

Food Serving Sizes

The DRI system draws upon the standard, or customary, USDA definition of food serving size data across foods. A table setting forth the DRI food category classification scheme, along with typical serving sizes is accessible here.

Methodology

A DRI value is the ratio of a pesticide’s dietary intake from a single serving of food, divided by the maximum acceptable daily intake for that pesticide, as determined by the EPA or other regulatory authority.

Put simply, the DRI is an index based on the relationship of estimated pesticide intake in a serving of food, relative to the maximum amount of the pesticide that a person can be exposed to in a day without exceeding the pesticide’s regulatory “level of concern.”

The EPA sets acceptable daily intakes for pesticide active ingredients, which are called in the U.S. “chronic Reference Doses” (cRfD).

In cases where the Agency imposes an added safety factor in response to the 1996 Food Quality Protection Act (FQPA), a pesticide’s cRfD becomes a cPAD, or “chronic Population Adjusted Dose.”

cPADs are “Adjusted” by the imposition of an additional, usually 10-fold safety factor to a pesticide’s cRfD, in order to more surely protect vulnerable population groups.

The dietary intake of pesticide from a single serving of food is determined by the pesticide’s measured concentration in the food, and the food’s typical serving size measured in grams.

The DRI system uses serving sizes known as Reference Amounts Customarily Consumed per eating occasion (RACCs). These quantities are set by the USDA.

As explained previously, there are three ways to calculate DRI values, each providing insights into different aspects of risk levels, distributions, and trends.

DRI-Mean (DRI-M) values are based on annual mean residue levels of only those samples with measured residues.

The Food Supply DRI (FS-DRI) is based on the annual mean residue level of all samples tested, but unlike the DRI-M, includes all samples with no quantified residue.

Individual-sample DRI values are particularly valuable for assessing the distribution of residue and risk levels across the supply of a specific food, grown in a given country using a known production system (conventional vs. organic).

Calculating DRI Values

For each year of testing, the US-PDP and UK-FSA report the following data for each tested food and pesticide:

  • N   Number of samples tested
  • NP   Number of samples in which a quantifiable residue was reported (number of positives)
  • %P   Percent positive (NP/N × 100%)
  • Mean   Mean of the positives; the annual mean residue concentration in the positive samples, always expressed in the DRI system in parts per million (ppm) by weight (e.g., mg/kg).

The DRI system uses the above data, coupled with the weight of a single serving of food (Serv) and a person’s body weight (BW), to calculate the three basic forms of DRI:

  • DRI-M Positive Sample Mean DRI = (Mean × Serv)/(cRfD × BW)
  • FS-DRI Food Supply DRI = (Mean residue × Serv)/(cRfD × BW) × N/NP = (DRI-M) × %P

In the case of individual sample results, and for each residue reported in a sample:

  • DRI = (Pesticide concentration × Serv)/(cRfD × BW)

In these equations, cRfD may be replaced by a cPAD or other ADI, as appropriate. Because they are ratios of two pesticide weights, DRI values are dimensionless.

Although DRI values can be calculated for a person of any weight, the DRI system currently uses as a default a 16-kg child. The selection of 16 kg (35.3 lb.) corresponds to children near 4-years-old, based on the 50th percentile in CDC growth charts (average of boys and girls).

Children consume a less diverse diet than adults, and eat relatively larger servings of the foods they do eat. In addition, children ingest more food per gram of body weight than adults, in order to support growth.

A child’s serving sizes (Serv) in the DRI system are estimated as 2/3 of the size of adult portions of food. Even though child serving sizes are smaller than adult serving sizes, children’s intake of food per serving is higher than for adults when expressed per kilogram of a child’s bodyweight versus an adult’s bodyweight.

While cRfDs and ADIs typically apply to the general population, they are sometimes estimated for subpopulations, e.g., infants, women of childbearing age, or individuals with certain genetic polymorphisms (e.g., PON-1).

When subpopulation cRfDs or ADIs are available, subpopulation-specific DRI values can be calculated via the DRI system.

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