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WHO Generic Risk Assessment Models for Vector Control Products

WHO Generic Risk Assessment Models for Vector Control Products

WHO develops and provides generic models that can be used for human health risk assessment of vector control products (VCPs). These documents are referred to as generic risk assessment models (GRAMs).  The GRAMs consider both adults and children of all age groups, as well as people in the following categories:

  • those handling products and preparing for application of the product;
  • those applying the products;
  • residents who may be exposed post-treatment.

In some cases, depending upon the product type and its use, the GRAM may include guidance on environmental hazard/risk assessment for the purpose of identifying potential risk to non-target organisms.

Generally, a risk assessment process involves three steps: hazard assessment, exposure assessment and risk characterization.

1. Hazard assessment is the identification of possible toxic effects of a substance, the dose/exposure levels at which those effects occur, and the dose/exposure levels below which no adverse effects are observed. Authoritative evaluations may be used as starting points for the risk assessment of VCPs. Examples of authoritative evaluations are:

  • Joint Meeting on Pesticide Residues (JMPR) ­– monographs and evaluations;
  • International Programme on Chemical Safety – concise international chemical assessment documents and environmental health criteria documents;
  • International Agency for Research and Cancer ­– monographs on the evaluation of carcinogenic risks to humans;
  • United States Environmental Protection Agency – pesticide evaluations;
  • European Food Safety Authority – pesticide risk assessments;
  • European Chemicals Agency – information on chemicals.

JMPR assessments, if available, will be used by PQT/VCP for risk assessment unless a more recent authoritative evaluation exists. As part of the hazard assessment process,  tolerable systemic dose levels (TSDs) are established. The critical NOAELs/LOAELs (or benchmark doses) (corrected for absorption) are divided by uncertainty factors (UFs) to account for variability and uncertainties. Thus, a TSD can be derived from long-term studies on oral toxicity. A tolerable systemic dose for acute exposure may also be derived to take into account acute exposure risks. A tolerable systemic dose is expressed in mg absorbed chemical/kg body weight per day. The determined mg absorbed chemical (Abs) may be a function of the oral, inhalation and/or dermal routes of exposure. 

TSD=Abs[point of entry] × N(L)OAEL/UF

2. Exposure assessment may concern insecticide operators, applicators, residents of treated dwellings and users of other treated buildings, bystanders, domestic animals, wildlife and the environment. Exposure is assessed in a “guideline scenario” which assumes that the product is used according to the instructions given on the product label and in WHO guideline information. Conservative high-end point estimates of the default distributions are used as defaults. No account is taken of intended misuse. All relevant routes of exposure are covered.

3. In risk characterization, estimates of exposure are compared with acceptable exposure levels previously defined in hazard assessment in all relevant exposure situations. The purpose of risk characterization is to examine the probability of adverse effects occurring during the use of the insecticide under defined exposure conditions. Risk characterization consists of comparing the estimate of total exposure (i.e. estimated systemic dose) with the tolerable systemic dose  established in the hazard assessment. Typically, the tolerable systemic dose is same as the acceptable daily intake or the chronic reference dose established for the active ingredients (GRAM, 2010). 

When the ratios are less than one, the health risk is acceptable. Ratios greater than one may indicate possible health risks, possibly requiring measures to reduce the risk. Changes may include modification of the recommended operational conditions, application rates or the amount of active ingredient in the formulated product. A risk-benefit analysis in which the risks of potential toxicity are compared with potential health benefits (e.g. disease prevention) may be needed in some cases (GRAM, 2010).

Ratio = Estimated Systemic Dose (mg/kg bw/day)
TSD (mg/kg bw/day)

Current WHO GRAMs