Chronic toxicity evaluation of pesticides

Sub-chronic toxicity tests are carried out to determine the repeated dose toxicity which usually run over a 90-day period. The chronic toxicity of a pesticide is determined by subjecting test animals to long-term exposure to the pesticide active ingredient. The possible adverse effects of chronic exposure to a pesticide include birth defects, production of tumors and neurotoxic effects. In order to evaluate the health risks from exposure to pesticides, the ADI which is the safe level of human exposure must be calculated first. ADI which means acceptable daily intake is considered to have no adverse effects on health even if consumed daily throughout one’s life. From the toxicity studies in animals, we can get the NOAEL the No-Observed Adverse Effect Level of a pesticide.

NOAEL is the highest exposure dose that does not cause toxic or adverse effect and is expressed as mg test pesticide per kg body weight of the test animal per day. Then, the NOAEL is divided by a safety factor to obtain an estimate of the ADI of a pesticide for humans. The safety factor is generally set at one hundred due to a safety factor of ten for dose conversion from animals to humans and another ten for the human variability. ADI is the maximum amount of a pesticide in food that can be ingested daily over a lifetime without harmful effects.

In order to evaluate the long-term dietary exposure assessment, the estimated dietary intake EDI of a pesticide residue is calculated by multiplying the pesticide residue level in the food by the amount of food consumed. Pesticide residue level can be obtained from supervised trials or the recommended Maximum Residue Levels. MRL is the highest level of a pesticide residue that is legally tolerated in or on food when pesticides are applied correctly. If the EDI is higher than the ADI, a risk to human health is suggested and the approval of pesticide may not be possible or withdrawn.

If the EDI is less than the ADI, the actual intake is considered to be lower than the ADI Which means that the use of the Pesticide meets safety standards. Many countries have their own individual MRLs. MRL for pesticide residues are established by crop field trials or by referring to other standards. The reference standards include international standards set up by Codex Alimentarius Commission which is a joint intergovernmental body of the United Nation’s FAO and WHO. Codex Alimentarius which means food code in Latin is a collection of international standards, codes of practice, guidelines, and other recommendations relating to foods, food production, and food safety.

The Codex Alimentarius is recognized by the WTO the World Trade Organization as an international reference for the resolution of disputable concerns about food safety and consumer protection. MRL established by European Union are often used as a reference standard. On the website of EU pesticides database, you can search MRL by selecting either a specific pesticide active substance or a specific agricultural product. And in Taiwan, we have our own MRL for Pesticide Residues in Foods which can be downloaded on the Taiwan FDA’s website. Here are tables from the downloaded document. This is a positive list of pesticides that are approved for use in specific agricultural product. For example, the pesticide 2,4-D can only be used on the commodities listed in the table.

It will be violation if 2,4-D is used on any product which is not listed in the table. Pesticides prohibited for use can also be found in this document.