by Sally Colby
Is there anything new or compelling about pesticide safety, or is it always the same information repeated in a different manner? What could someone say about pesticide safety to capture your attention?
Dr. Mark Matocha, associate professor and Extension specialist with the Ag and Environmental Safety Unit of Texas A&M, believes understanding toxicity and toxicology makes pesticide safety more interesting. Matocha defined modern pesticides as “chemicals or substances that are toxic to living organisms so they can control pests.”
“Toxicology is the study of poisons,” said Matocha. “Pesticide toxicology is the ability of synthetic pesticides to cause adverse effects on biological organisms. Any chemical, including any pesticide, can pose risks to people, animals or the environment.”
Matocha reviewed essential toxicology terminology. “Toxicity refers to the innate potential of a substance to cause injury,” he said. “Hazard describes the potential to cause injury under a specific set of circumstances. Risk is the potential and likelihood to cause harm; a function of the magnitude of exposure or contamination along with the hazard.” Risk is the main safety consideration because it refers to the probability that something – a pesticide or any other chemical – will cause harm.
Other important terms include risk assessment – determining the hazards of a substance as well as potential exposures and the likelihood of adverse effects. “Risk assessments in the United States are mandated by statutory and regulatory law,” said Matocha. “This is a mostly science-based activity – we start with a hypothesis, which leads us to a prediction. We then conduct experiments, make observations, collect data and analyze to come up with a risk assessment.”
Risk management refers to the social endeavor of avoiding adverse effects. Risk management is mandated by statutory law, implemented by administrative law and is influenced by politics, economics and social goals.
The EPA has had primary jurisdiction for regulating pesticides in the U.S. since 1970. It conducts risk assessments to estimate the probability of harm from using products. “It begins by identifying hazards,” said Matocha. “That leads to a dose-response relationship study using scientific experiments to determine which dose will cause no effect, which dose will cause an adverse effect and which dose will cause death. Risk characterization also includes exposure assessments, which studies the expected dose from product use and environmental residues.”
Toxicity and exposure are key to the most important principle in toxicology: the dose makes the poison. These aspects apply to the person who mixes the product, the applicator and laborers in the area where the product is mixed and used.
The LD50 (or lethal dose) is a quantitative measure of toxicity and determines the dose at which 50% of the population will be killed from a one-time dose of the substance. “The lower the LD50 value, the more toxic the chemical,” said Matocha. “A low LD50 indicates that it takes a smaller dose to have a lethal effect.”
The toxicity of a substance can’t be manipulated or changed, but those working with chemicals can limit exposure to substances with appropriate PPE to prevent dermal, inhalation and oral exposure. PPE requirements vary by product, so anyone handling pesticides should check labels for those requirements. “Labels have been developed by the manufacturer and the EPA to make sure they provide the appropriate level of safety requirements for mixers, loaders and those working in the vicinity of pesticides,” said Matocha. “The label will have requirements for PPE as well as any other restrictions or precautions.”
PPE should never be stored with pesticides. Maintain a separate area for PPE, including respirator cartridges. Clothing worn during mixing or applying pesticides should be washed separately, and heavily contaminated clothing should be discarded. Avoid the risk of accidental ingestion by only storing pesticides in their original containers and not food or beverage containers.
Dermal (skin) exposure to chemicals is not equal on all body parts – the thick skin on palms and soles absorbs less than the thinner skin in the ear canals and armpits. For this reason, gloves are likely the most important piece of PPE. Research has shown that workers mixing pesticides received 85% of total exposure on their hands and 13% on their forearms. The same study showed that wearing protective gloves reduced pesticide exposure by 99%.
“I’m not saying all you need to worry about is gloves,” said Matocha, adding that pesticide labels indicate whether gloves should be used. “I’m highlighting the importance of gloves, but other pieces of PPE can be equally important depending on what you’re using.” It’s important to wear the proper gloves – gloves that have any level of absorbancy will not reduce exposure. Gloves that are the most resistant to chemicals are usually made of nitrile.
Limit inhalation exposure by avoiding breathing dust and droplets or vapor and always wear a respirator if indicated. When labels indicate the use of protective eyewear, there may not be specific recommendations on appropriate eyewear. Options include goggles, face shields, safety glasses with shields or full-face respirators. Respirators are either air supplying or air purifying – choose the correct type for the job and use one only after a fit test according to the Worker Protection Standard. Respirator equipment should be cleaned after each use.
Workers should be familiar with basic first aid for pesticide poisoning and be aware that symptoms can be confused with other health problems such as heat stress, heat exhaustion or heat stroke. “If in doubt, seek professional medical attention,” said Matocha. “Get as much documentation as you can, such as the pesticide label and the Safety Data Sheet (SDS), and take it to the medical provider so they have a good starting point for appropriate medical attention.”
LD50 values, along with signal words and signs, are used to denote hazard levels on pesticide labels. “Category I have the highest toxicity and are marked with the skull and crossbones,” said Matocha. “They will have ‘danger’ on the label. These are highly toxic or highly corrosive products that would not take much of a dose to cause adverse effects. Category II will have ‘warning’ as the signal word and are moderately toxic.” Category III will have “caution” on the label. Category IV is the least toxic and may have “caution” on the label.
Product labels include information about storage and disposal. When the label indicates disposal options, it’s up to the user to abide by both state and federal requirements.
Use a triple rinse procedure for rinsing used pesticide containers prior to disposal and/or recycling. First, drain the remaining contents into the spray tank for at least 30 seconds to remove as much of the concentrated chemical as possible. Next, fill the container one-third full of water, place the cap on the container and rotate or shake to rinse all sides. Drain the rinse mixture from the pesticide container into the spray tank. Repeat the rinse, shake and drain two more times before disposing of the container. If a high-pressure rinse nozzle is available, it can be used to bypass the triple rinse.
Matocha made one last important point that could potentially prevent an environmental disaster: Be sure the fill hose remains above the level of liquid while filling the tank to prevent backflow and potential contamination.