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Pesticide Exposure and Neurodevelopment in the Fetus. Marcel Elizondo July 2009 STEER Student UTHSCSA-Harlingen. Pesticides. What is a pesticide?

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pesticide exposure and neurodevelopment in the fetus

Pesticide Exposure and Neurodevelopment in the Fetus

Marcel Elizondo

July 2009 STEER Student

UTHSCSA-Harlingen

pesticides
Pesticides
  • What is a pesticide?
    • According to the EPA, a pesticide is “any substance or mixture of substances intended for preventing, destroying, repelling, or mitigating any pest”
  • What about pests?
    • Pests are “living organisms that occur where they are not wanted or that cause damage to crops or humans or other animals”4
pesticides4
Pesticides
  • Some examples of pests include:
    • Pests include mosquitoes, beetles, ants
  • How do pesticides kill pests?
    • Pesticides attack the nervous system of the pests which in turn leads to their untimely demise5
elimination of pesticide use
Elimination of Pesticide Use
  • Stockholm Convention on Persistent Organic Pollutants
    • This agreement was signed by 90 countries in 2001 to eliminate the use of 12 POPs including DDT
    • The World Health Organization made an exception in 2006 to back the use of DDT to control malaria in certain countries2
pesticide use
Pesticide Use
  • In the US, our agricultural areas use more than 75% of conventional pesticides
  • Exposure to pesticides has been linked to preterm birth and reduced fetal growth
  • A popular pesticide used to be dichlorodiphenyltrichloroethane (DDT), which was subsequently banned in the US in the 70’s
  • Currently, replacement pesticides for DDT are insecticides such as organophosphates.1
effects of some pesticides
Effects of Some Pesticides
  • Organochlorines (i.e. DDT)
    • Excitation of central nervous system which leads to tremors, hyperexcitability and convulsions (both tonic and clonic)
  • Organophosphate (i.e. insecticides)
    • Act by inhibiting the acetylcholinesterase in synaptic clefts1
organophosphate detection
Organophosphate Detection
  • Exposure to organophosphates is usually measured by nonspecific metabolites in urine known as dialkyl phosphate (DAP) metabolites1
human studies
Human Studies
  • Center for the Health Assessment of Mothers and Children of Salinas (CHAMACOS)
    • Research is funded by NIH and EPA
    • Four objectives of CHAMACOS
    • Six hundred and one pregnant woman were recruited in 1999-2000. They were at least 18 years old and were less than 20 weeks in their gestation period2
chamacos
CHAMACOS
  • Neonatal neurodevelopment was tested using the Brazelton Neonatal Behavioral Assessment Scales (BNBAS)
  • Maternal serum samples of DDT and DDE were higher than the National Health and Nutrition Examination Survey reference population
  • A minor negative association was observed between maternal DDE serum levels and abnormal infant reflexes2
chamacos14
CHAMACOS
  • Most other studies conducted had similar results to the CHAMACOS study
    • One exception was a study in North Carolina with a birth cohort of 912 infants
    • In utero exposure discovered that higher levels of DDE in the cord serum and breast milk led to hyporeflexia
    • This exception is noted because a similar (although smaller) cohort in Oswego, NY was conducted and the North Carolina findings could not be replicated2
spanish study
Spanish Study
  • Cohort of 92 children
  • Exposed to high levels of DDE
  • Had lower social, mental and psychomotor development (assessed using Griffiths Scales of Infant Development and BSID-II)2
mexican study
Mexican Study
  • DDE exposure in utero
  • Study found a decrease in psychomotor development using BSID-II at 3, 6 and 12 months2
common theme
Common theme
  • The common result from the CHAMACOS, Spanish, and Mexican studies suggests that DDE may have a negative effect on psychomotor development in infants less that 12 months of age
  • Only the North Carolina cohort had a positive association with decreased mental development at 6 months of age2
how bad can pesticide exposure be
How Bad can Pesticide Exposure Be?
  • First, we need to determine what the “environment” in relation to pregnancy
    • One known example of a hazardous environmental toxin is tobacco smoke
    • The neonatal “environment” can include nutrition, adequacy of prenatal care, smoking, alcohol use, maternal age and socioeconomic conditions
    • Two or more of these factors might be related or synergistic3
physical environmental
Physical Environmental
  • A mother’s physical environmental is what most of us are familiar with
    • Air, water, food, soil and a number of consumer products
  • A mother’s placenta is thought of to protect a fetus against any toxins encountered, however some cases have shown the placenta to actually magnify hazardous maternal exposures3

Santa Ana Wildlife Reserve

physical environmental20
Physical Environmental
  • For some persistent and bioaccumulative exposures (i.e. organochlorine pesticides), fetal exposure can occur as a result of maternal body burdens from years of preconceptional exposures
  • Fathers are just as accountable for exposures since their preconceptional exposures contribute to the risk through a mutagenic mechanism involving the sperm3
neurodevelopmental effects
Neurodevelopmental Effects
  • Not specifically targeting pesticide exposure, environmental contaminants have been known to have adverse effects on brain and neurological development
    • Some developmental disabilities include ADHD, learning disabilities, autism, mental retardation and effects on the nervous system
    • Studies have shown that the window of susceptibility is with prenatal exposures
    • “Toxicological studies link both prenatal and postnatal exposure to organophosphate pesticides to neurodevelopmental effects”3
limitations
Limitations
  • This research focused on prenatal exposure and not on adolescent or adult effects
future research
Future Research
  • Due to limited human population studies of pesticide exposure, more research is needed particularly with preconception exposures. This research should include both maternal and paternal exposures.
recommendations
Recommendations
  • One recommendation for the detection of pre-exposure to the fetus
    • Include a questionnaire during prenatal care about possible environmental exposures for the expectant parents
  • This environmental assessment should be particularly conducted in agricultural communities where pesticide exposure is more prominent
references
References
  • Rosas, L.G. and Eskenazi, B. (2008). Pesticides and Child Neurodevelopment. Current Opinion in Pediatrics, Vol. 20, 191-197.
  • Eskenazi, B., Rosas, L.G., Marks, A.R., Bradman, A., Harley, K., Holland, N., Johnson, C., Fenster, L., & Barr, D.B. (2008). Pesticide Toxicity and the Developing Brain. Basic & Clinical Pharmacology & Toxicology, Vol. 102, 228-336.
  • Stillerman, K.P., Mattison, D.R., Giudice, L.C., & Woodruff, T.J. (2008). Environmental Exposures and Adverse Pregnancy Outcomes: A Review of the Science. Reproductive Sciences, Vol. 15 (7), 631-650.
  • US Environmental Protection Agency. About pesticides. 2006. Available at: http://www.epa.gov/pesticides/about/index.htm. Accessed July 25, 2009.
  • American Pregnancy. Pesticides Exposure During Pregnancy. 2009. Available at: http://www.americanpregnancy.org/pregnancyhealth/pesticides.html. Accessed July 25, 2009.