The Causes of Autism

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Prenatal Pesticide Exposure Linked to Lower IQ: Findings from A California Study

Who are the spectaculous authors, what is the title of the study, and when was it published?

Authors: Robert B. Gunier, Asa Bradman, Kim G. Harley, Katherine Kogut, and Brenda Eskenazi

Title: Prenatal Residential Proximity to Agricultural Pesticide Use and IQ in 7-Year-Old Children.

Year: 2017

What is the study about?

A study examining the associations between prenatal pesticide exposure and neurodevelopmental outcomes reveals adverse effects on children’s performance on developmental assessments, IQ scores, and attention measures. California-based studies have reported links between organophosphates and autism, Parkinson’s disease, and neural tube defects. The findings highlight the potential impact of agricultural pesticide use on children’s cognitive development. Additionally, the study explores the interaction effects of heavy metals and pesticides, providing valuable insights into the detrimental effects on living organisms. Related research within the library focuses on biomarkers, oxidative stress, and detoxification mechanisms in relation to autism and neurodevelopment.

What previous research do the authors cite on this topic?

Adverse associations have been observed between prenatal maternal dialkylphosphate (DAP) concentrations and children’s performance on the Bayley Scales of Infant Development at 2 years (Eskenazi et al., 2007), measures of attention at 5 years (Marks et al., 2010), and on the Wechsler Intelligence Scale for Children (WISC) at 7 years (Bouchard et al., 2011a). Several studies conducted in other populations have similarly reported adverse associations between prenatal exposure to OP pesticides and child neurodevelopment (Engel et al., 2011; Rauh et al., 2011).


In addition, several epidemiologic studies conducted in California have shown that higher nearby agricultural pesticide use is associated with various adverse health outcomes. For instance, OP and fungicide use have been associated with Parkinson’s disease (Costello et al., 2009; Wang et al., 2011), organochlorine pesticide use with autism (Roberts et al., 2007), and the use of carbamates (benomyl and methomyl) and the neonicotinoid imidacloprid with neural tube defects in children (Rull et al., 2006; Yang et al., 2014).

A recent study conducted in Spain utilized residential proximity to agricultural fields as a measure of pesticide exposure and observed an inverse relationship between postnatal hectares of crops near the residence and Full-Scale IQ, Verbal Comprehension, and Processing Speed in children aged 6 to 11 years (González-Alzaga et al., 2015). Additionally, higher concentrations of pyrethroid metabolites in children’s urine have been linked to increased behavioral problems (Oulhote and Bouchard, 2013) and attention deficit/hyperactivity disorder in one study (Wagner-Schuman et al., 2015), although another study did not find such an association (Quirós-Alcalá et al., 2014). Previous research has also shown inverse associations between children’s cognition and levels of manganese in blood and hair (Riojas-Rodríguez et al., 2010; Bouchard et al., 2011b; Menezes-Filho et al., 2011).

What are the methods?


This study focused on pregnant women enrolled in California’s low-income health care program between October 1999 and October 2000. With an initial enrollment of 601 pregnant women, the study assessed the neurodevelopment of 330 children at the age of seven. The analysis was further refined to include 283 children who met specific criteria, including known prenatal residential location for at least 75 days per trimester during pregnancy and availability of neurodevelopmental assessments at 7 years of age. Twins (10), children with relevant medical conditions (4), and those without prenatal measurements of DAP metabolites (2) were excluded. As a result, the final study population used for analysis consisted of 283 children, providing valuable insights into the relationship between prenatal care and neurodevelopmental outcomes.

Dependent Variables

Full Scale IQ obtained through the Weschler Intelligence Scale for children.


The study examined a variety of neurotoxic pesticides with agricultural use in the study area (Monterey County, CA) during the prenatal period, including fifteen OPs and six carbamates, two manganese (Mn)-based fungicides (maneb and mancozeb), eight pyrethroids, and one neonicotinoid (imidacloprid).

What are the findings?


The most heavily used type of pesticide was Organophosphates (OPs), followed by Manganese fungicides (Mn-fungicides).

For individual OP pesticides, the average use (GM) ranged from 5 kg for malathion to 23 kg for diazinon, and these five pesticides were moderately to highly correlated, meaning that when the use of one increased, the use of the others tended to increase as well.

The average use (GM) of the other neurotoxic pesticide groups ranged from 4 kg for neonicotinoids to 54 kg for Mn-fungicides.

There was a moderate to high correlation between the use of the five different neurotoxic pesticide groups within one kilometer of the maternal residence during pregnancy, meaning that when the use of one group of pesticides increased, the use of the other groups also tended to increase.


The researchers found that exposure to neurotoxic pesticides during the prenatal period was associated with lower Full-Scale IQ scores in children at 7 years of age. In particular, there was a statistically significant inverse association between exposure to organophosphate pesticides and Full-Scale IQ, with a 2.8-point decrease in IQ for each standard deviation increase in organophosphate exposure.

There was also a significant inverse association between exposure to all neurotoxic pesticides combined and Full-Scale IQ, with a 2.0-point decrease in IQ for each standard deviation increase in estimated exposure.

A 1-SD increase in toxicity-weighted OP pesticide use during pregnancy was also associated with a 2.9-point decrease in Verbal Comprehension scores.

Specific Pesticides and IQ

When looking at individual OP pesticides, the study found that exposure to acephate and oxydemeton-methyl was significantly associated with a decrease in Full-Scale IQ. There was also a significant negative relationship between agricultural use of acephate, chlorpyrifos, diazinon, and oxydemeton-methyl and verbal comprehension.

However, there was no relationship between the use of chlorpyrifos, malathion or diazinon and Full-Scale IQ.

What are the implications of this study?

Singh et al. (2017) analyzed the interaction effect between heavy metals and pesticides, reviewing at length their detrimental effect on living organisms. See the diagrams below.

Singh N, Gupta VK, Kumar A, Sharma B. Synergistic Effects of Heavy Metals and Pesticides in Living Systems. Front Chem. 2017 Oct 11;5:70. doi: 10.3389/fchem.2017.00070. PMID: 29075624; PMCID: PMC5641569.
Singh N, Gupta VK, Kumar A, Sharma B. Synergistic Effects of Heavy Metals and Pesticides in Living Systems. Front Chem. 2017 Oct 11;5:70. doi: 10.3389/fchem.2017.00070. PMID: 29075624; PMCID: PMC5641569.

What other research within the library is this study related to?

Adams et al. (2009) found that variations in the severity of autism could be partially explained by the urinary excretion of toxic metals and initial glutathione.

Zhao et al. (2023) found that children with autism had higher concentrations of molybdenum, cadmium, tin, and lead were found in the whole blood of ASD cases compared to control subjects.

El-Ansary et al. (2020) found that there was a complete separation of autistic and control participants using nine biomarkers, which provides insight into the possible pathophysiology of the autism, particularly in relation to oxidative stress, energy metabolism, mitochondrial dysfunction, and apoptosis.

Al-Yafee et al. (2011) found multiple significant differences in the autism group on several metabolic biomarkers related to sulfur-dependent detoxification mechanisms, which are involved in the detoxification of neurotoxins and oxidative stress.

Can I read the full study?

Sure. Right here.

Shh. Quiet in the hall.

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