Topic Area: Agriculture

Geographic Area: Salinas Valley, California

Focal Question: What are the results of pesticide regulations designed to reduce poisoning of farmers and farm workers?


Sunding, David and Joshua Zivin, 2000, “Insect Population Dynamics, Pesticide Use, and Farm worker Health,” Journal of Agricultural Economics, 82.3 (August 2000): 527-540.

Zilberman, David, et al., “The Economics of Pesticide Use and Regulation,” Science, New Series, 253.5019 (2 August 1991): 518-522.

“Acute Poisoning Following an Exposure to Agricultural Insecticide—California,” Center for Disease Control,

Reviewer: Stephanie Hicks, Colby College ‘03


The public is becoming more and more concerned with the use of chemicals on agricultural products and the health effects that these pesticides have on farm worker health (Sunding and Zivin, 2000).  In 1984, the state of California reported 1,156 farm worker illnesses that were most likely related to pesticide use (Center for Disease Control).  Increased concern about worker safety and public health has precipitated much debate over the regulation of pesticide use (Zilberman, et al., 1991).


Mevinphos, an organophosphate insecticide used to control aphids, mites, grasshoppers, cutworms, leafhopper caterpillars and other insects, is applied to a variety of vegetables, such as head lettuce, leaf lettuce, cauliflower, broccoli, and celery.  In the Salinas Valley of California, located on the central coast of the state, mevinphos is applied primarily to leaf lettuce.  Mevinphos poisonings are usually caused by acute exposure to the pesticide and result in more serious illnesses than any other insecticide currently in use.  From 1982 to 1991, 548 mevinphos-related illnesses were reported in California.  68 of these cases resulted in hospitalization and 201 resulted in lost workdays.  Symptoms include nausea, diarrhea, vomiting, pinpoint pupils, tremors, and, in the worst cases, paralysis.  Certain workers, such as harvest workers, experience more exposure to the pesticide than other workers, such as those who install irrigation equipment (Sunding and Zivin, 2000).


When deciding to use mevinphos, farmers take certain conditions under consideration, such as the insect population, cost and output price of the pesticide, and regulations regarding the use of the pesticide.  Farmers then consider profit levels and compare expected profits with and without the use of the pesticide.  Finally, farmers evaluate the threshold level at which the insect population will affect the marketability of the leaf lettuce.  All of these factors play a role in the decision to apply mevinphos to crops (Sunding and Zivin, 2000). 


Bans on pesticides constitute the primary form of pesticide regulation used in the United States.  However, the success of pesticide bans depends on the availability of substitutes. Without substitutes, bans result in lower production levels, higher prices, and a loss in farmer income.  However, other methods, such as partial bans, restrictive-use policies, and pesticide taxes may result in health benefits without as many economic costs (Zilberman, et al, 1991).


In the Salinas Valley, both pesticide taxes and regulation of the time period between pesticide application and harvest have been used in an effort to decrease the number of farm worker illnesses caused by contact with mevinphos.  Increasing the pre-harvest interval (PHI) is designed to decrease the exposure of farm workers to harmful chemicals by allowing the pesticide to decay before farm workers come in contact with it. However, this may also alter the amount of pesticide that is needed and may result in an overall increase in the amount of pesticide used.  While increasing the PHI is designed to reduce exposure to the insecticide, taxes on pesticides are designed to increase the cost of using the pesticide.  Efficient taxes, those set equal to the marginal benefit derived from risk reduction, reduce the use of pesticides but do not affect exposure to the chemical (Zilberman, et al., 1991 and Sunding and Zivin, 2000). 


Risk to farm laborers is measured by contamination, exposure, and physical symptoms.  Exposure is defined by “units of square centimeters of plant surface area per kilogram of body weight per day.”  Contamination is defined as “the product of the share of acres treated with the pesticide, the amount of the chemical used per acre treated and a crop-specific coefficient” (Sunding and Zivin, 2000).


In Salinas Valley, increasing the PHI decreased exposure to the pesticide because the increased time period allowed the chemical to decay, thus decreasing its risk to workers.  However, because the increased PHI allows the pesticide to decay, the amount of pesticide used may increase, thereby increasing contamination.  The results for Salinas Valley found that, despite the incentive to use more of the pesticide, the decrease in exposure offset the increase in contamination so that the number of poisonings decreased by 0.79 cases per unit increase in PHI.  Increasing the tax on mevinphos use decreased contamination, but did not affect exposure to the pesticide.  However, the tax also resulted in an overall decrease in worker poisonings (Sunding and Zivin, 2000).  The effects of pesticide taxes are similar to those for partial-bans on pesticide use by “encouraging farmers to become more selective in their chemical choices and to switch to other options as they become relatively more cost-effective” (Zilberman, et al, 1991). An increase in the PHI has a greater affect on overall profit than does a tax on pesticide use because “it does not affect expected crop damage at the margin.”  In Salinas Valley, extending the PHI reduced profit by $1.84 million per poisoning avoided while the tax decreased profit by $3.51 million per case (Sunding and Zivin, 2000).


The case of Salinas Valley shows that, while evaluating pesticide regulation, it is important to take multiple factors into consideration.  For example, if economists only examine insect population at the time of pesticide application, then harvest conditions and factors will be overlooked.  As David Sunding and Joshua Zivin note, “It is important for economists to pay attention to insect population dynamics when assessing pesticide productivity and the impact of pesticide regulations like the PHI that alter the timing of pesticide use” (Sunding and Zivin, 2000).