On a sunny, hot day in June a 4-year-old girl and her mother arrive at the emergency department after the girl experienced 3 brief episodes, each lasting 2–3 seconds, of shaking, staring and verbal unresponsiveness during the hour before arrival. There was no loss of consciousness or incontinence. The girl has been vomiting and complaining of abdominal discomfort for 2 hours and has a rash on her arms and face that began 4 hours before presentation. She has no history of head injury or seizure disorder and has been previously healthy. Direct questioning reveals no likely exposure to amphetamines, cocaine, isoniazid, lidocaine, lithium, MDMA (3,4-methylenedioxymethamphetamine [“ecstasy”]), PCP (phencyclidine), phenytoin or tricyclic antidepressants. The child is afebrile, her pulse 120 beats/min, her blood pressure 80/60 mm Hg and her respiratory rate 26 breaths/min. She is awake but not talking spontaneously. Neurological examination and examination of the ears, nose and throat, the chest and the abdomen reveal no abnormalities. A fine maculopapular rash is apparent on the face, neck, arms and lower legs. After arriving in the emergency department the child has a further episode of shaking and verbal unresponsiveness. Knowing that a toxic exposure is one possible cause, the physician quickly takes an environmental exposure history using the CH2
mnemonic (Community, Home, Hobbies, Occupation, Personal habits, Diet and Drugs; for children the occupation question refers to workplace contaminants brought into the child's environment)1
to identify possible exposures ().
Questions surrounding this case: Could any of the exposures have caused the child's symptoms? What investigations should be ordered? Who should be consulted for advice if needed?
Pesticides are chemical substances used to kill animal, insect, plant and fungal pests in agricultural, domestic and institutional settings.2
The main groups of commonly used pesticides include herbicides, insecticides, fungicides, fumigants and rodenticides (). The organochlorine, organophosphate and carbamate insecticides are of particular concern because of their toxicity and persistence in the environment.2,3
Organochlorine insecticides were banned for agricultural and domestic use in Europe and North America because of environmental effects, but they are still used in developing countries and continue to linger in the environment because of their chemical stability. Studies in the Canadian Arctic have shown that insecticides and herbicides persist 3 to 8 times longer in cold temperatures than in temperate climates.3
Pesticide toxicity can result from ingestion, inhalation or dermal absorption. Outdoor spraying of pesticides poses the obvious risk of inhalation, but pesticide exposure by inhalation also occurs indoors.
The primary routes of exposure for most Canadians, however, are by ingestion of small quantities found in most of the foods we eat,4,5
or by skin absorption through direct contact with surfaces that accumulate pesticide particles.2
Imported foods are noteworthy because they receive pesticide treatment not only during growth, but also during storage and shipment. One example is citrus fruit that is protected against rots and moulds with fungicides; otherwise long distance transport would be more difficult. The Pest Management Regulatory Agency of Health Canada reviews and registers products under the authority of the Pest Control Products Act and determines the amount of pesticide residue that is allowed on a food commodity. About 250–300 pesticide chemicals are registered in Canada for use in production or handling of various foods.5
Maximum residue limits have been established for 100 of these. The remaining chemicals include those too toxic for any residues on foods to be permissible, those unlikely to leave any residue because of their chemical nature and those of such low toxicity that no residue limits need be established for them.
Selected agricultural food commodities in Canada are monitored for pesticide residues. Between 1994 and 1998, 1.2% of domestic foods and 2% of imported fresh products had levels exceeding the maximum residue limits established in the Pest Control Products Act.4
In an Ontario study that tested pesticide residues from 1991 to 1995, 4% of both domestic and imported fruits and vegetables exceeded the maximum allowable residue.4
These percentages are small and on the surface seem acceptable. However, concerns have been raised by physicians and scientists4,6,7
as to the adequacy of the methodology and standards used by the Canadian and US governments both for the release of pesticides and for the acceptance of pesticides used on foods. Setting standards for single chemicals may not reflect the true biological impact of multiple exposures and cumulative effects. For example, a recent study of cumulative dietary pesticide intake in children living on farms and those not living on farms in Washington State found that acceptable chronic dietary doses were exceeded in 56% and 44% of the children respectively.8
Although one insecticide or herbicide may be deemed safe at a particular level, the average Canadian-grown peach may contain residues of several of these pesticides.6
Most of these pesticides interfere in some way with neurotransmission, resulting in an aggregate, if not synergistic, effect. When setting standards, the combined effects of multiple residues plus coincident exposures from other food, water and air sources must somehow be considered. The child dietary pesticide study8
provides a promising model for the use of biological monitoring of exposure to achieve this goal. The Canadian Pest Management Regulatory Agency is currently revising its risk assessment process to account for current shortcomings in risk assessment pertaining to aggregate exposures, cumulative effects and the specific risks of pediatric exposures, among others. Until then, it is advisable to practise precautionary medicine by recognizing groups of patients at increased risk of health effects from pesticide exposure.6