TOXICITY AND RISK ASSESSMENT Pesticides are toxic compounds that may cause adverse effects on the human and the

1.6 TOXICITY AND RISK ASSESSMENT Pesticides are toxic compounds that may cause adverse effects on the human and the

environment. Toxicity has been defined as the capacity of a substance to produce harmful effects, and other terms used in the risk assessment of chemicals are hazard, defined as the potential to cause harm, and risk, defined as the likelihood of harm. Risk characterization is the estimation of the incidence and severity of the adverse effects likely to occur in a human population, animals, or environmental compart- ments due to actual or predicted exposure to any active substance.

Humans can be exposed to pesticides by direct or indirect means. Direct or primary exposure normally occurs during the application of these compounds and indirect or secondary exposure can take place through the environment or the ingestion of food. Figure 1.4 summarizes the main routes of indirect exposure to pesticides.

A complete set of data is needed for the toxicological and ecotoxicological evaluation of pesticides.

FIGURE 1.4 Routes of indirect exposure to pesticides.

Pesticides: Classification and Properties 33 Regarding the human health assessment, toxicological studies need to include

the following tests:

A: Acute toxicity, which involves harmful effects in an organism through a single or short-term exposure, should be studied by:

1. Dermal toxicity test: Rabbits are employed more often than any other species for studies of skin toxicity, although guinea pigs, rats, or mice

are also used. The results are expressed in terms of LD 50 , the dose under which the conditions stated will cause death in 50% of a group of test animals.

2. Mucus membrane and eye toxicity test: The conjunctiva of the eye and the vaginal vault of experimental animals (rabbits and monkeys) have been employed in tests of the toxic or irritant effects of chemical substances on mucus membrane.

3. Inhalation toxicity test: The procedures for the evaluation of potential hazards of gases, dusts, mists, or vapors via the inhalation route vary depending on the physical nature (solubility, particle size) of the pesticide.

4. Oral toxicity test: The procedure normally employs the administration of compounds in the diet or intragastrically by gavage. The advantage is that it allows precise measurement of daily dosage to body weight. The oral toxicity generally takes place in three stages, acute (short-term), subacute (subchronic), and chronic (long-term).

B: Repeated dose test that comprises the adverse effects occurring in experi- mental animals as a result of repeated daily dosing with, or exposure to, a pesticide for a short part of their expected life span.

C: Reproduction and teratology that involves the endocrinological changes associated with the reproductive cycle in the female and the anabolic systems involved in embryologic and fetal growth constitute a challenging background against which to test the toxic potentiality of a pesticide where the enzymatic system plays an important role.

D: Carcinogenesis is to identify the carcinogenicity potential of pesticides in laboratory animals. The studies must be sufficient to establish the species and organ specificity of tumors induced and to determine the dose –response relationship. For nongenotoxic carcinogens, they identify doses that cause no adverse effects.

Estimation of a no observed adverse effect level (NOAEL), when possible, or of

a lowest observable adverse effect level (LOAEL) is a critical step in the toxico- logical risk assessment of pesticides [14]. Concerning ecotoxicity, the estimation of hazard to wildlife involves the deter- mination of the effects on different species. Toxicity data should be gathered for soil organisms, beneficial arthropods (as honeybees), aquatic species (fish, inverte- brates, algae, and microorganisms), terrestrial vertebrates (mammals and birds), and plants. Several end points are of interest, depending on the species, namely acute toxicity, growth and activity inhibition, bioconcentration, and effects on reproduc- tion. The poisoning of the species depends on the concentration of the pesticide in

34 Analysis of Pesticides in Food and Environmental Samples different environmental compartments (e.g., water, air, and soil), and consequently a

predicted environmental concentration (PEC) has to be derived and compared with the corresponding predicted no effect concentration (PNEC).

Therefore, the toxicological and ecotoxicological effects as well as the concen- tration of pesticides in the environmental compartments and in food are required for the risk assessment of pesticides. The presence of pesticides in these matrices is normally referred to as pesticide residues, which are defined as any original or derived residue, including relevant metabolites, from a chemical. Analytical methods to determine pesticide residues in the mentioned matrices with adequate sensitivity and selectivity are then needed.

The analysis of pesticide residues in food and environmental samples, together with their monitoring in those matrices, will be described in the following chapters of this book.