Section I APC: Anthropogenic Chemicals and Activities

Food: Pesticide Contamination

Introduction

How much pesticide residue did I eat today?

No more than necessary, and less than would be detrimental to your health.

Government authorities must be able to support the answer to the consumer’s question with scientific data and valid scientific studies.¹¹¹ The “no more residues than necessary” concept originates from the principle of good agricultural practice, which implies that the desired effect (pest control) will be achieved without leaving more residues than necessary in the food.

Before Registration

Pesticide residue evaluation and risk assessment prior to registration are summarized in Figure l.^12,31

Risks to the environment and to the user are also evaluated but are not considered further under the present topic—food contamination with pesticide residues.

Metabolism studies on a pesticide in crops and farm animals identify the nature of the residue. The residue may consist of a parent compound or metabolites or a mixture. In some cases, different pesticides produce the same metabolites; in other cases, the metabolite of one pesticide is another pesticide. Some crops genetically modified for herbicide resistance achieve their resistance by metabolizing the herbicide to a derivative with no herbicidal activity.

The acceptable daily intake (ADI) of a chemical is the daily intake, expressed on a body-weight basis, which, during an entire lifetime, appears to be without appreciable risk to the health of the consumer on the basis of all the known facts at the time. The ADI is based on animal feeding studies that find the daily dose over a lifetime resulting in no observable adverse effect on the most sensitive animal species tested. Then, a margin of safety (safety factor, commonly 100) is applied to allow for extrapolation from animals to humans and the variability in responses between average and highly sensitive humans.

FIGURE 1 Risk assessment process before registration for pesticide residues in food. ADI: acceptable daily intake; Acute RfD: acute reference dose; MRL: maximum residue limit or tolerance.

Source: Hamilton DJ, Food contamination with pesticide residues, in Encyclopedia of Pest Management, 2002, p 287.

The acute reference dose (acute RfD or ARfD) of a chemical is an estimate of the amount normally expressed on a body-weight basis, which can be ingested in a period of 24 hours or less without appreciable health risk to the consumer on the basis of all known facts at the time of the evaluation. The acute RfD is also based on the results of animal dosing studies with a suitable safety factor.

The maximum residue limit (MRL), synonymous with “tolerance,” is the maximum concentration of pesticide residue legally permitted in or on food commodities. The MRL usually applies to the commodity of trade, which may or may not be the same as the edible portion. For a fruit such as apples, it is the same, while for bananas, the MRL applies to the whole banana, but only the pulp is eaten. An MRL provides a division between food that is legally acceptable or unacceptable. Foods derived from commodities complying with the relevant MRLs are intended to be toxicologically acceptable, but the MRL is not a dividing line between safe and unsafe.

Supervised residue trials on animal feed commodities and livestock feeding studies with pesticide residues generate the information required to support MRLs for meat, milk, and eggs.

Risk assessment tells us whether or not the amounts of residue are likely to be safe for consumers.¹⁴-⁵¹ We estimate dietary intake (also referred to as “dietary exposure”) of pesticide residues by multiplying the level of residue in the food ready for consumption by the amount of the food consumed. For chronic risk assessment, we compare the sum for all foods of expected long-term average intake with the ADI for the pesticide. For acute risk assessment, we compare possible intake from high consumption of a food, in a period of 24 hours or less, with the acute RfD.

After Registration

The design of monitoring studies for residues in food commodities depends on the purpose: random survey of food consignments (surveillance), targeted enforcement sampling where a residue problem is suspected, export monitoring to meet trade requirements, and total diet studies.

Government authorities regularly survey agricultural and animal products for levels of pesticide residues. If the label directions were based on reliable and representative field trials and if users are

Food: Pesticide Contamination

5

faithfully following label directions, then residues will be within the legal MRLs. Most surveys have demonstrated a high level of compliance.

Total diet studies identify which pesticides and measure in what quantities people are actually consuming. Food purchased in the marketplace is prepared by peeling and cooking as in the normal household and is then subjected to residue analysis. Amounts of foods consumed are known from specially designed food surveys for subpopulations such as adult males and females, children, toddlers, and infants, as well as for ethnic groups and regions or localities. Dietary intakes for populations and subpopulations are calculated from the diets and the residue levels found by analysis. Commonly, total diet studies demonstrate intakes much less than the ADI.

Food Processing

Food processing usually reduces pesticide residue levels because of the washing or cleaning, peeling, milling, juicing, cooking, or baking. Residue levels may increase in some processed commodities because the residue tends more to one fraction than another.¹⁶¹ For example, residues on the surface of a wheat grain will find their way into the bran fraction with little in the flour. Residues of oil-soluble pesticides will find their way mainly into the vegetable oil fraction from an oilseed such as soybean.

In particular cases, a food process can change the nature of the residue. For example, ethylenebisdi- thiocarbamate fungicides are converted, on cooking, to ethylenethiourea, which is more toxic than the parent pesticide. Fortunately, ethylenebisdithiocarbamates are essentially surface residues, and their levels can substantially be reduced by thorough washing before a cooking or blanching step.

Trade Issues

MRL values derived from good agricultural practice are, by their nature, local. A pesticide is used in the best way within local cultural practices to control a specific pest, and the rate of pesticide disappearance depends on local environmental conditions. Comparisons among countries of national MRLs and tolerances will frequently reveal substantial differences. Table 1 shows the range of MRLs for ethephon in 17 countries for each of four commodities.

TABLE 1 National Ethephon MRLs and Tolerances (mg/kg) in 1999¹"!

The differences pose problems for international trade in food commodities. The importing country may reject shipments of food that do not comply with its national MRLs. It is attractive for some lobby groups and some governments to use national differences in MRLs as a barrier to trade.

Where no MRL or tolerance has been set for a pesticide on a food, some national governments apply a “zero tolerance,” that is, the MRL is assumed to be zero unless otherwise stated. The reason no MRL is set could simply be that the pest problem does not occur or that the crop is not produced locally; for example, cold temperate countries do not produce pineapples, so there will be no local uses or local MRLs.

The Codex Alimentarius Commission was established in 1961 to implement the FAO/WHO Food Standards Program. A purpose of the program is to protect the health of consumers and to ensure fair practices in the food trade. The Codex Committee on Pesticide Residues (CCPR) has the responsibility to establish Codex MRLs for food commodities in international trade.

CCPR relies on the data supplied by member governments and has established many MRLs. The methods of data evaluation in Codex are very similar to the methods in countries with regulatory control of pesticide use; Codex draws on the expertise of scientists from such countries around the world. Member government acceptance of Codex MRLs for food commodities in international trade is reducing the incidence of trade barriers based on national MRLs.

Developing countries have sometimes suffered pesticide residue trade difficulties because a lack of resources has made it difficult for them to monitor their exports effectively to ensure compliance with the importing country MRL requirements.

Analytical Methods for Pesticide Residues

Analytical methods for pesticide residues in food typically rely on gas-liquid chromatography (GLC) or high-performance liquid chromatography (HPLC) in the final measurement step following extraction from the sample and a sequence of clean-up steps.^12,81 Multiresidue methods include many residues in one procedure for the sake of economy. Monitoring usually requires the detection and quantitative measurement of residue levels down to concentrations of around 0.01-0.05 mg/kg. Laboratories must validate their procedures down to the required level, that is, prove that the procedures can identify and measure with a specified precision residues down to a required “limit of quantification” (LOQ).

The LOQ is important in the interpretation of monitoring data. An analytical result reported as “less than LOQ” or sometimes as “no detectable residue” could possibly mean no residue or a residue at a level too low for the method.

Not all pesticide residues are amenable to inclusion in multiresidue methods; they may need separate analysis, which becomes expensive. Reports of monitoring data should state explicitly which residues would have been detected if present above stated LOQs.

Reliable high-quality data are essential for correct interpretation during registration, investigation, and control of residues in food. Highly skilled analysts using good laboratory practices, standard procedures, and other measures are generating valid data to support those requirements.

Future

The science of risk assessment will be further developed. Food safety and food security will continue to be important for consumer, government, and industry.¹⁹¹ Trade issues will continue to be problematic with specific incidents of residues in foods arising from time to time. National governments will develop strategic approaches to deal with trade issues related to pesticide residues. Knowledgeable people in government and industry and experienced workers in functioning laboratories will be needed to support those strategic approaches. Exporters will need to monitor residues in a high percentage of their exports to meet the requirements of their customers. We might expect more developments with biopesticides. Relevant impurities in biopesticides are more likely to be biological than chemical, posing new challenges for analytical and test methods.

References

• 1. Frehse, H. ed. 1991. Pesticide Chemistry, Advances in International Research, Development, and Legislation, Proceedings of the Seventh International Congress of Pesticide Chemistry (IUPAC), Hamburg, 1990. VCH Verlagsgesellschaft mbH: Weinheim, Germany; 361-601.
• 2. FAO. 2016. Submission and Evaluation of Pesticide Residues Data for the Estimation of Maximum Residue Levels in Food and Feed; third edition. FAO Plant Production and Protection Paper, 225:1-286.
• 3. Dishburger, H.J., Ballantine, L.G., McCarthy, J., Murphy, J. and Tweedy, B. G., eds. 1991. Pesticide Residues and Food Safety: A Harvest of Viewpoints. ACS Symposium Series 446, American Chemical Society: Washington, DC, 1-348.
• 4. Hamilton, D.J., Holland, P.T., Ohlin, B. et al. 1997. Optimum use of available residue data in the estimation of dietary intake of pesticides. Pure Appl. Chem. 69:1373-1410.
• 5. WHO. 2009. Principles and Methods for the Risk Assessment of Chemicals in Food, IPCS. Chapter 6, Dietary Exposure Assessment of Chemicals in Food. Environmental Health Criteria 240.
• 6. Holland, P.T., Hamilton, D., Ohlin, B. and Skidmore, M.W. 1994. Effects of storage and processing on pesticide residues in plant products. Pure Appl. Chem. 66:335-356.
• 7. FAO. 2000. Pesticide Residues in Food. Ethephon. Evaluations 1999. FAO Plant Production and Protection Paper, 157:210.
• 8. Ambrus, A. 1999. Quality of Residue Data. In Pesticide Chemistry and Bioscience: The Food- Environment Challenge, Brooks, G.T. and Roberts, T.R., eds., 339-360. The Royal Society of Chemistry: Cambridge.
• 9. Ambrus, A. and Hamilton, D. 2017. Chapter 12, Future Directions. In Food Safety Assessment of Pesticide Residues, Ambrus, A. and Hamilton, D., eds., 507-510. World Scientific Press: Singapore.