QAL Laws & Regulation Practice Exam

When mixing two organophosphate pesticides, how is the Restricted Entry Interval (REI) established?

1. Add the two REIs together

2. Add the longest REI and then 50% of the next longest

3. Use the shortest REI of the two pesticides

4. Calculate the average of the two REIs

The correct answer is: Add the longest REI and then 50% of the next longest

The process for establishing the Restricted Entry Interval (REI) when mixing two organophosphate pesticides involves considering the potential cumulative exposure from both substances. The correct approach is to take the longest REI and add 50% of the next longest REI. This method accounts for the fact that each pesticide may have different toxicological effects and varying times at which they might remain hazardous on treated surfaces. Choosing the longest REI ensures that the maximum safety period required for the most toxic pesticide is respected, while adding a portion of the next longest REI acknowledges that the second pesticide also contributes to overall risk. This combinatory assessment is necessary because organophosphates can act synergistically, amplifying the potential health impacts beyond what would be expected if they were used separately. Other methods, such as simply using the shortest REI or averaging the two, do not sufficiently safeguard against exposure risks associated with the combined use of these chemicals. The approach of adding just the REIs together also fails to address the varying levels of toxicity and the potential for increased risk when residues from both pesticides may still be present together. Thus, this method ensures a more comprehensive protective measure for individuals who may come into contact with treated areas.