The role of agrochemicals in modern agriculture is continuously evolving, and their contribution to crop protection continues to increase. Linking science and policy is a cornerstone of the work of both the regulatory authorities and industry. Before a pesticide becomes available on the market, most countries insist that national authorities must evaluate that pesticide thoroughly to ensure that it will not harm health or the environment. Pesticides that pass this evaluation are granted a license or registration that permits their sale and use according to regulations.
Pesticides are widely used in producing food and feed. Their residues may remain in small amounts in or on agricultural produce and processed foods. To ensure the safety of food, most governments regulate the maximum level of each permitted pesticide residue.
Most countries have been pursuing a policy of economic development for the past 20 years or more, and deterioration of the global environment has accelerated. In June 1992, a summit meeting of 118 countries agreed to organize internationally for basic legislation regarding the environment. This agreement was called the "Rio Declaration". The goal of the declaration was to protect the environment while achieving economic development, thus attaining sustainable development of the global economy. Since then, various kinds of meetings have been held to work out a solution for environmental problems related to agriculture. One of these, the OECD Joint Meeting of the Agriculture/Environment Committee, developed 13 indicators for assessing the effect of agricultural activity on the environment, with a particular focus on pesticide use and risk indicators.
This paper deals with the current status of pesticides in relation to food safety and environmental protection, and the future outlook.
Overview of Pesticide Residues
Food Safety in Relation to the Codex Alimentarius
All over the world, an increasing number of consumers and most governments are becoming aware of food quality and safety issues, and are realizing the need to be selective about the foods which people eat. It is now common for consumers to demand that their governments take legislative action to ensure that only safe food of acceptable quality is sold, and that the risk of food-borne health hazards is minimized. Since the first steps were taken in 1961 to establish a Codex Alimentarius, the Codex Alimentarius Commission — the body charged with developing a food code — has drawn world attention to food quality and safety. For more than three decades, all important aspects of food pertaining to the protection of consumer health and fair practices in the food trade have come under the Commission's scrutiny.
In order to foster consumer protection worldwide, there have been several Agreements internationally on food safety. The United Nations General Assembly Guidelines for Consumer Protection in 1985 stated that.
- " When formulating national policies and plans with regard to food, Governments should take into account the need of all consumers for food security and should support and, as far as possible, adopt standards from the FAO's ... and the WHO's Code Alimentarius...".
The FAO/WHO Conference on Food Standards, Chemicals in Food and Food Trade (in cooperation with GATT) in 1991 agreed that:
- "The process of harmonizing national food regulations to bring them into line with international standards and recommendations was an urgent one, which needed to be accelerated..." and that
- "Provisions essential for consumer protection (health, safety of food, etc) should be the focus of emphasis in Codex Standards...".
The Agreement on the Application of Sanitary and Phytosanitary Measures and the Agreement on Technical Barriers to Trade in 1995 formally recognized international standards and recommendations, including the Codex Alimentarius, as reference points for facilitating international trade and resolving trade disputes in international law. The FAO World Food Summit in 1996 agreed to:
- "Implement policies aimed at ... improving physical and economic access by all, at all times, to sufficient, nutritionally adequate and safe food and its effective utilization" and to "Apply measures, in confirmity with the Agreement on the Application of Sanitary and Phytosanitary Measures and other relevant international agreements, that ensure the quality and safety of food supply...".
Codex Alimentarius has held more than 30 meetings since 1963, and has achieved a number of agreements ( Table 1).
Pesticides have a central position in Codex activities. In particular, maximum residue limits of pesticides (MRLs) in and on foods and feeds have become national food safety standards for member countries. However, MRLs act as potential barriers in the international trade of agricultural produce. This is because the way in which pesticides are used varies from country to country, while levels of pesticide applications depend on climatic conditions. In addition, MRLs also vary according to the intake of different types of food in different countries. Fig. 1 shows how MRLs for pesticides are set.
The No Observed Effective Level (NOEL) of a pesticide is determined by the data from a series of toxicological studies using test animals. The intake considered a safe amount is ingested by the test animals over their whole life span with no observable ill effect. ADIs are established by the WHO/FAO Expert Committee, but are basically the NOEL with a 1/100 safety level. MRLs are determined by taking into account the food intake, the average body weight of human beings, and pesticide residue levels under good agricultural practices. A problem in establishing international MRLs is that daily intake of particular food commodities is quite different from one country to another depending on dietary customs.
For this reason, MRLs set by the Codex Alimentarius Commission are a reference, not a directive, for individual countries. As an example, the MRL for carbaryl for several foods in selected countries is shown in Table 2.
In general, pesticide manufacturers are concerned mainly with their profits. For this reason, they pay special attention to pesticides for major crops which are grown by many farmers, such as rice, apple and Chinese cabbage. In recent years, Korean farmers have began to grow minor crops or wild herbs such as leopard plant or parsley in greenhouses all year round. Farmers usually apply pesticides in order to ensure product quantity as well as quality. However, no proper pesticides are available on the market for these crops, because pesticide companies do not bother to register promising pesticides for crops with a relatively small cropping area. Furthermore, if a pesticide is not registered for a particular crop, the Korean Food and Drug Administration (KFDA) adopts the lowest registered MRL for that crop. As a result, when KFDA is monitoring residue levels on minor crops, permitted levels are based on the lowest value. This means that residues in harvested produce may exceed the MRL, so that the crop is not accepted for marketing.
In the United States, trials of reasonable pesticide levels for minor crops are handled by a Federal-State Project known as the "Inter-regional Research Project No. 4", or IR-4. For the past three decades, its task has been to conduct field trials and collect data needed for EPA approval of so-called "minor-use" pesticides.
The Korean government has been implementing since 1998 a national project called "Pesticide registration trials for minor crops". Biological activity and residues were tested for a total of 65 combinations of pesticides and crops. As an output of the trials, 20 pesticides for eight crops were registered in 1999, and 39 pesticides for 13 crops were registered in 2000. Reasonable MRLs for registered pesticides in or on minor crops were also set by the Joint Committee on Pesticide Residues. In addition, KFDA recognized that a wide variety of different vegetables are available in Korea. It decided to group vegetable foods into leaf, fruit, and root vegetables. For example, the MRL of Procymidone in perilla leaves was changed from 0.2 mg/kg to 5 mg/kg, based on the MRL for lettuce. The MRL in perilla leaves has now been further increased, to 10 mg/kg. (Note: Perilla is an ornamental plant with edible purple or green leaves).
The safety of exported agricultural produce is a major issue in international trade. Basically, residue levels for exported agricultural produce should be compatible with the MRLs of the importing country. However, some countries, including United States, operate zero tolerance for residues of pesticides which have not been registered by their own government. Thus, trace amounts of residues in imports may cause the shipment to be rejected. Some examples of Korean exports rejected in this way are: chlorthalonil in pear in 1989, procymidone in ginseng in 1995, dichlorvos in cucumber in 1995, and monocrotophos in citrus in 1996.
If a certain pesticide is essential to prevent damage from specific pests in specific export crops, and if it is not registered in the importing country, an alternative pesticide must be developed, or a tolerance level for imports must be established. Pesticides which often cause residue problems in internationally traded agricultural produce are those used for post-harvest treatments, low (chlorpyrifos) or no Codex MRLs, and pesticides which are not registered in major world markets. They include chlorthalonil, vinclozolin, iprodion, captan/folpet, thiabendazole, dithiocarbamate, carbendazim, imazalil, procymidone, methamidophos, omethoate, diazinon, pyrimiphos-methyl, azinphos-methyl, permethrin, monocrotophos, parathion-methyl, mevinphos, phosmet, esfenvalerate, malathion, and methidathion.
Results from monitoring pesticide residues in fruits and vegetables by EU member countries showed that regardless of the country concerned or the sample size, the proportion of agricultural produce with residues over the MRL was around 1% of the monitored samples ( Table 3).
The pesticide residue monitoring data for Korean domestic produce show that the percentage of samples with residues over the Korean MRL has been falling in recent years ( Table 4).
Food Quality Protection Act, Usa
The 1996 Food Quality Protection Act (FQPA) of the United States established a new standard of safety for pesticide residues in food, with an emphasis on protecting the health of infants and children. There must be "reasonable certainty" that "no harm" will come to infants and children or other sensitive individuals exposed to pesticides. All exposure to pesticides in food, drinking water, and home and garden use must be considered in determining permissible levels of pesticides in food.
EPA has met an important deadline in the new law by issuing a schedule showing how the Agency will reassess more than 9,700 existing "tolerances" — or MRLs in foods — by August 2006. Pesticides that appear to pose the greatest risks will be considered first.
Many pesticides, even when they are properly applied in accordance with label directions, may leave residues in or on treated fruits, vegetables, grains, and other commodities. Though pesticide residues often decrease over time as food crops are washed, stored, processed, and prepared, some residues may remain in both fresh produce (such as apples or tomatoes) and processed foods (such as applesauce or tomato ketchup). EPA has classified into three groups the 469 pesticides which are to be evaluated.
Group 1 contains the 228 pesticides that appear to pose the greatest risk to public health. These have top priority, and will be examined first. They include organophos-phates, carbamates and organochlorine classes of chemicals; probable and possible human carcinogens; high-hazard inert ingredients; and any pesticides for which normal usage exceeds their reference dose (RfD) (i.e.the amount believed not to cause adverse effects if consumed daily over a 70-year lifetime). Protection of infants and children is given high priority. Of the approximately 1,800 organophosphate tolerances receiving priority review, over 300 are for residues on crops that are among the top 20 foods consumed by children.
This group contains 93 pesticides that are possible human carcinogens but which are not included in Group 1, and all remaining pesticides subject to re-registration. These have the second-highest priority for review.
The 148 pesticides in this group include most of the biological pesticides, inert ingredients, and recently registered pesticides with tolerances that are not subject to re-registration pesticides with active ingredients registered since 1984.
Process of pesticide dissipation
Various parameters are involved in the environmental fate of pesticides applied to the target. In principle, all chemicals, including pesticides, which are introduced into the environment are gradually recycled within and between the bio-, geo-, atmo-, and hydro-spheric systems ( Fig. 2). The rate at which pesticides are moved and dissipated is closely related to the physico-chemical parameters of the chemical itself and surrounding environmental conditions. The latter factors include application time and dose, land use patterns and target crops. Factors related to climate and weather include temperature, rainfall, evapo-transpiration rates and wind velocity. Parameters related to soil are run-off characteristics, organic carbon content, texture, hydraulic characteristics and pH.
Several schemes have been proposed for the assessment of the degradability of pesticides in soil. The IUPAC commission on agrochemicals proposed that the half-life in soil be used for assessing the degradability of pesticides ( Table 5). Half-lives, DT-50 and DT-90 values have also been introduced by some regulatory authorities (United States, EPA 1982; Denmark, AEP 1988; Germany, BBA 1990) as triggers in tiered persistence testing systems ( Table 6). In addition to DT-50 and DT-90 values, the evaluation criteria used by BBA of Germany include the percentage of active ingredients or metabolites left in the soil before the next application, the percentage of bound residues formed, and the normal rate of application.
Since the 1980s, a large number of mathematical models have been developed which attempt to simulate the fate of pesticides in the soil. Research into the interplay of factors affecting the fate and mobility of pesticides in soils has developed rapidly over the past 15 years. The development of simulation models has proved useful, both in guiding experimentation and in integrating, testing and improving our understanding of the dynamic and complex nature of the soil-plant-pesticide system. Pesticide leaching models are also now being used for management purposes by both industry and public authorities as part of the registration process.
The use of models implies a different set of needs and priorities. The two most important are ease of setting parameters and the reliability of predictions. To some extent, these requirements are conflicting, since reliability implies the need for mechanistic models. These minimize "model error", but at the cost of increasing the demand for data.
Despite many differences in detail, the most commonly used models of pesticide mobility have much in common in their general approach, since they are all attempting to represent the same phenomena. Table 7 summarizes some models used for pesticide leaching in the unsaturated soil zone.
Protection of water sources is one of the most effective ways of reducing the entry of toxic substances into the water supply. Among the many chemicals encountered in drinking water, pesticides occupy a unique position, since they are deliberately manufactured and used. WHO (World Health Organization) has formulated drinking water guidelines for some 40 pesticides.
Tolerable daily intake (TDI) was derived in the traditional manner by dividing the no-observed-adverse-effect level (NOAEL) or the lowest-observed-effect level (LOAEL) for the critical effect by an uncertainty factor accounting for interspecies and intraspecies variation. The guideline value (GV) was derived from the TDI by multiplying it by body weight (bw; 60 kg for adults, 10 kg for children, 5 kg for children, 5 kg for infants) and the proportion of total intake accounted for by drinking water (P; 10% by default if no data exist), and divided by the daily drinking water consumption (C; 2 liters for adults, 1 liter for children, 0.75 liter for infants). This gives the formula:
GV = TDI x bw x Guidelines P/C for the TDI of common pesticides in drinking water are summarized in Table 8.
One of the biggest problems in water supplies is the short-term presence of a high concentration of a pesticide in drinking water. If, for example, a particular pesticide is found in drinking water at a level higher than the standard, a decision has to be made as to whether the pesticide is a greater risk than turning off the water supply. And despite current concerns about endocrine disrupting chemicals (EDs), it is not clear that drinking water is a major source. Many EDs are hydrophobic. If they are present in raw water, they can be easily removed by treatment.
Persistent Organic Pollutants (Pops)
Persistent organic pollutants (POPs) are organic compounds that, to a varying degree, resist photolytic, biological and chemical degradation. POPs are often halogenated. Characteristically, they are not very soluble in water but are highly soluble in fat, so they accumulate in fatty tissues. They are also semi-volatile, and can move long distances in the atmosphere before deposition occurs. These properties of unusual persistence and semi-volatility, coupled with other characteristics, have resulted in the presence of compounds such as PCB all over the world, even in regions where they have never been used. They have been measured on every continent, including sites such as the open ocean, deserts, the Arctic and the Antarctic where no significant local sources exist. The only reasonable explanation for their presence in such areas is long-range transport from other parts of the globe.
Halogenated carbons are a major group of POPs. Of these, the organochlorines are by far the most important group. Included in this class of organohalogens are dioxins and furans, PCBs, aldrin, endrin, dieldrin, hexachlorobenzene, mirex, toxaphene, heptachlor, chlordane, and DDT. The use of halogenated, and particularly chlorinated organic compounds has become entrenched in contemporary society. They are used by the chemical industry in the production of a broad array of products, ranging from polyvinyl chloride (millions of tons per year) to solvents (several hundreds of thousands of tons), to pesticides (tens of thousands of tons) and specialty chemicals and phamaceuticals (from thousands of tons to kilogram quantities). In addition, human and natural processes add to the production of undesirable by-products and emissions (such as chlorinated dioxins) often characterized by their persistence and resistance to breakdown.
Immunotoxicity in association with exposure to different POPs has been reported by several authors. Investigators have demonstrated immune dysfunction as a plausible cause for increased mortality among marine mammals. They have also demonstrated that the persistent consumption by seals of a diet contaminated by organic pollutants may lead to vitamin and thyroid deficiencies, and make the animals susceptible to microbial infections and reproductive disorders. Exposure to POPs has been correlated with population declines in a number of marine mammals, including common seals, harbor porpoises, bottle-nosed dolphins and beluga whales. The scientific literature has demonstrated a direct cause and effect relationship in mink and ferrets between PCB exposure and immune dysfunction, reproductive failure, increased kit mortality, deformation and adult mortality.
It is difficult to establish whether human exposure to POPs has a direct effect on disease incidence. As with wildlife species, humans encounter a broad range of environmental exposures, frequently to a mixture of chemicals at any one time. Studies of the incidence of cancer associated with occupational exposure to 2,3,8-TCDD seems to indicate that extremely high-level exposures of human populations do elevate overall cancer incidence. More recently, research has been accumulating which suggests a possible relationship between exposure to some POPs and human disease and reproductive dysfunction.
For a chemical to be identified as a POPs, it must have the following features:
- Persistence: The ability to resist degradation in various media such as soil, water or sediments, measured as the half-life of the substance in the medium;
- Bioaccumulation: The ability of a chemical to accumulate in living tissues to levels higher than those in the surrounding environment;
- Toxicity: The ability of a chemical to cause injury to humans or the environment;
- Volatility: The ability of a chemical to vaporize into air;
- Measurements of the chemical in remote regions: Considered by some to be critical for identifying a chemical as a persistent organic pollutant of global concern;
- Bioavailability: Based on field data or expert judgment, this has also been proposed as a criterion for identifying POPs.
Funding global negotiations to establish a global treaty on POPs is a challenging task. The international community is responding to the need for resources by contributing through an innovative financial mechanism known as the POP's Club. Donations and pledges have been received from Australia, Austria, Canada, Denmark, Finland, Germany, Madagascar, the Netherlands, Norway, Sweden, Switzerland, the United Kingdom, the United States, and the International POPs Elimination Network.
Fig. 3 shows the procedure for identifying POPs by assessing the physico-chemical parameters and global survey data of the candidate chemicals.
Endocrine Disrupting Chemicals (Eds)
During the 1990s, there has been increasing concern about reproductive abnormalities in wildlife, the increase of breast cancer in women, and the falling sperm counts in men. Many scientists have suggested that the underlying cause is the pesticides and other chemicals that disrupt the endocrine system. The endocrine system plays a critical role in normal growth and development and in reproduction. Even small disturbances in endocrine function can have a profound and lasting effects. Meanwhile, at present, scientific knowledge is inadequate to inform public policy. US/EPA estimates that there are approximately 87,000 chemicals to be screened for possible endocine disrupting activity. These include about 900 active ingredients of pesticides; 2,500 other ingredients used to formulate pesticide products; 75,500 industrial chemicals; and 8,000 cosmetics, food additives and nutritional supplements. The initial sorting stage will separate chemicals into four categories based upon a review of all existing relevant scientific information as shown in Fig. 4.
Category 1: No testing necessary now — Hold. Category One includes chemicals such as strong mineral acids and bases, amino acids, sugars, certain polymers (approximately 3,000 polymers), etc., that are unlikely to exhibit endocrine activity and need not be screened. For example, polymers with an average molecular weight of more than 1,000 daltons are unlikely to be able to cross biological membranes and barriers, and would therefore not be biologically available to influence the endocrine system.
Category 2: Insufficient data for Tier 1 screening. Category Two consists of chemicals for which there are insufficient data to determine their potential for endocrine activity. Chemicals with insufficient data will undergo priority setting for Tier 1 Screwing, which may include High Throughput Pre-screening (HTPS). HPTS is presently being examined by EPA to determine if suitable technologies can be developed for routine application in Tier 1 Screening. Prescreening is necessary, because it is estimated that up to 62,000 chemicals may belong to this category.
Category 3: Direct move to Tier 2 testing. Category Three includes those chemicals that have sufficient data to bypass screening, but need testing. Chemicals with sufficient data to bypass Tier 1 Screening will go directly to Tier 2 Testing. EPA estimates that there are more than 1000 chemicals in this category, and a similar number in the next (Hazard Assessment)
Category 4: Direct move to hazard assessment. The final category contains substances for which there is adequate data, which will be referred to the appropriate agency for hazard assessment.
At present, no chemicals are designated as endocrine disrupting substances on a global basis, although there are several candidates. However, the list of candidates is quite different in different organizations. The National Environment Research Institute, the national agency responsible for monitoring endocrine disrupting chemicals in Korea, follows the list announced by the World Wildlife Fund, which involves 67 chemicals. This include 44 pesticides, 17 of which are still available on the market. However, their production has been falling in recent years ( Table 9).
Multi-disciplinary studies have mainly focused on monitoring the chemicals from an agricultural and environmental point of view. Korea's National Environmental Research Institute is responsible for monitoring water, sediments, air, and dioxins from waste incinerators. The Korean FDA is responsible for monitoring disposable bowls for instant noodles, tin cans, etc. The National Institute for Agricultural Science and Technology (NIAST) is responsible for monitoring agricultural produce, arable soil and irrigation water.
Regulations governing pesticides have been characterized by a number of trends in recent years. There is a demand for more data on food and environmental safety, coupled with increased international efforts to achieve global accords. The big challenge now is the costly re-registration program, designed to ensure that older, but still widely used, products meet today's environmental and safety standards. The social, political and regulatory situation surrounding the crop protection industry has become much more complex during the last decade. People living in modern society play the role of active and involved consumers. They are concerned about the safety, price, availability, and quality of their food. These demands must be reconciled by farmers, regulators, policy makers, and farm input industry, pesticide manufacturers. In spite of a new interest in biological pest control, chemical control is likely to remain the backbone of crop protection over the next decade.
Future pesticides must meet the following criteria. They must be effective and active with low doses of less than 5 g/ha. They must degrade rapidly and completely after their job is done. They must not leave toxic residues in or on food, or damage the environment. They must not be transferred away from the target location. They must be produced by methods of manufacturing, formulation and packaging, and applied in ways that minimize waste and exposure. They must not disturb the treated ecosystem in any undesirable way.
In order to ensure the safety of our food and keep our environment healthy and clean, there must be a constant exchange of information between international bodies and national regulatory agencies. Similarly, each country must regularly monitor pesticide residues on a national basis to determine trends in the levels of toxic substances in and on food, feeds and the environment. Finally, scientific data on residues and other aspects of chemical use must be open to the public, to satisfy the right-to-know of citizens.
- BBA. 1990. Guidelines for the Official Testing of Plant Protection Products. Biological Research Center for Agriculture and Forestry, Germany.
- Brooks, G.T. and T.R. Roberts. 1999. Pesticide Chemistry and Bioscience. The Food - Environment Challenge. The Royal Society of Chemistry, London, United Kingdom.
- DK AEP. 988. Application Concerning Active Ingredients. National Agency of Environmental Protection, Copenhagen, Denmark.
- Eisenbrand, G., M. Hofer, R. Kroes and L. Shuker. 2000. Assessing health risks from environmental exposure to chemicals. The example of drinking water. Food and Chemical Toxicology 38: Suppl. 1. 1998. Committee on Environment and Natural Resources, National Science and Technology Council, USA.
- Endocrine Disruptors: Research Needs and Priorities.
- Endocrine disruptor screening program, Initial sorting. 1999. Office of Science Coordination and Policy, US/EPA.
- Honeycut, R.C. and D.J. Schobacker. 1994. Mechanisms of Pesticide Movement into Groundwater. CRC Press Inc., United States.
- Implementing the Food Quality Protection Act. 1999 . EPA 735-R-99001.
- Pesticide Re-registration Progress Report for 1997. 1998. EPA 783-R-98-003.
- Roberts, T.R. and P.C. Kearney. 1995. Progress in Pesticide Biochemistry and Toxicology. Vol. 9. Environmental Behaviors of Agrochemicals. John Wiley & Sons.
- Ritter, L., K.R. Solomon and J. Forget. 1995. An assessment report on: DDT-Aldrin-Dieldrin-Endrin-Chlordane-Heptachlor-Hezachlorobenzene-Mirex -Toxaphene-Polychlorinated Biphenyl-Dioxins and Furans. The International Programme on Chemical Safety.
- FAO. 1997. Understanding the Codex Alimentarius. 1997. FAO International Division.
- UNEP Chemicals. 1998. Persistent Organic Pollutants (POPs). UNEP Chemicals (IRPTC), Geneva, Switzerland.
- UNEP Survey on sources of POPs. 1996. IFCS expert meeting on persistent organic pollutants, Manila, Philippines. (Unpub. mimeograph).
- US EPA. 1982. Pesticide assessment guidelines, Subdivision N, Chemistry: Environmental fate, NTIS PB83-153973, Springfield, VA, United States.
- Vighi, M. and E. Funari. 1995. Pesticide Risk in Groundwater. CRC Press Inc., United States.
Index of Images
Figure 1 Schematic Flow to Establish the MRLS of Pesticides Used for Food Commodities
Figure 2 Environmental Fate and Dissipation Processes of Applied Pesticides
Figure 3 Flow Chart of Pops Identification Procedure
Figure 4 Screening Program in United States, Endocrine Disrupters for Organized by Us/Epa
Table 1 Results Achieved from Codex Alimentarius Activities
Table 2 Comparison of the MRL for Carbaryl for Selected Foods in Some Countries
Table 3 Number of Fruit and Vegetable Samples Analyzed for Pesticide Residues in Europe (Eu, 1996) Showing the Sample Numbers Analyzed Per Head of Population
Table 4 Percentage of Korean Agricultural Produce with Residues Over the MRL, 1998-2000
Table 5 Ranking of Pesticide Persistence in Soil
Table 6 . Regulatory Triggers for Soil Degradation Testing
Table 7 List of Current Leaching Models for Pesticides in Unsaturated Soils
Table 8 Risk Assessment of Some Selected Pesticides in Food and Drinking Water
Table 9 Annual Production of 17 Pesticides Suspected of Having Endocrine Disrupting Activities, Korea
Download the PDF. of this document, 161,951 bytes (158 KB).