In recent decades, neurodevelopmental disorders in humans have been occurring with increasing frequency; for this reason, the disciplines of epigenetics, epidemiology, and environmental toxicology (Abbasi, 2016, Alabdali et al., 2014, Bellinger, 2012, Bennett et al., 2016, Boivin et al., 2015, Braun et al., 2006, Emerson et al., 2014, Eshraghi et al., 2018, Eubig et al., 2010, Freitag et al., 2012, Geier et al., 2009, Grandjean and Landrigan, 2006, Grandjean and Landrigan, 2014, Grandjean et al., 2017, Hamza et al., 2019, Herbert, 2010, Koufaris and Sismani, 2015, Lanpheur, 2015, Lao, 2014, Lyall et al., 2014; Project TENDR, 2016; Schuch et al., 2015, Sealey et al., 2016, Tran and Miyake, 2017, Van Mil et al., 2014, Walton et al., 2017) have seen growing interest in the interaction between genetic predisposition and environmental risk factors in various neurodevelopmental disorders. According to the fifth edition of the Diagnostic and statistical manual of mental disorders (American Psychiatric Association, 2013), neurodevelopmental disorders are classified as intellectual disabilities, communication disorders, autism spectrum disorders (ASD), attention deficit hyperactivity disorder (ADHD), specific learning disorders, and motor disorders, among others.

The prevalence of these disorders has increased over the last few years, according to official statistics. Several studies show a decrease in the intelligencel quotient (IQ) of the population in many countries (Dutton and Lynn, 2013, Dutton and Lynn, 2016, Dutton et al., 2017a, Dutton et al., 2017b). In addition, according to a longitudinal study on intellectual disability (ID) carried out by Karam et al. (2016), its etiology can be classified as environmental in 44 % cases, genetic in 20.5 %, idiopathic in 12.6 %, secondary to neonatal sequelae in 13.2 %, and/or secondary to other diseases in 9.2 %. They conclude that since 44 % of ID is of environmental origin, environmental factors should be addressed to reduce the prevalence of ID. On the other hand, in the U.S. in 2017, the National Statistics Center provided results showing an increase in the estimate for 2014–2016 of children diagnosed with any of the neurodevelopmental disorders (Zablotsky et al., 2017). Based on this study, during 2014–2016, the percentage of children between the ages of 3 and 17 who had ever been diagnosed with a developmental disability increased from 5.76 % to 6.99 %. This upward trend in the prevalence of neurodevelopmental disorders is confirmed in a new 2015–2018 study by the National Statistics Center showing that children living in rural areas were more likely to be diagnosed with a developmental disability (19.8 %) than those living in urban areas (17.4 %) (Zablotsky and Black, 2020). In consonance with Danielson et al. (2018), approximately 6.1 million Americans between the ages of 2–17 were diagnosed with ADHD in that year, conforming to statistical data obtained from parent surveys. This went from 4.4 million in 2003 to 6.1 million people diagnosed (9.4 %) in 2016. This number included 338,000 children aged 2–5 years, 4 million aged 6–11 years, and 3 million aged 12–17 years.

The Public Health Agency of Canada published its 2015 autism prevalence study, studying 40 % of the 5–17-year-old population in 7 of Canada's 13 provinces, and establishing the prevalence rate at 1 in every 66 children in 2015 (Canadian Public Health Agency, 2018). The Canadian Public Health Agency is also conducting a comparative study of autism prevalence per thousand in three regions: Quebec, Newfoundland and Labrador, and Prince Edward, from 2003 to 2015. In 2003 the autism rate per thousand in Prince Edward was 5, in Newfoundland and Labrador it was 6, in Quebec 7, whereas in 2015 the autism rate per thousand in Prince Edward was 17, in Newfoundland and Labrador 19, and in Quebec it was 13, showing a continuous increase in all these years. According to data from the Centers for Disease Control and prevention, in 2014 the rate of autism in 8-year-olds in 11 U.S. states was 1 in 59 children born (Baio et al., 2018), in 2016 providing an official rate of 1 in 54, assuming a 10 % increase from 2014 to 2016 (Maenner et al., 2020, Centers for disease control and prevention (CDC), 2020) and in 2018 the reported rate was 1 in 44, implying a 23 % increase from 2016 to 2018 (Maenner et al., 2021). A study published on July 5, 2018, in California (Nevison et al., 2018) analyses various statistical sources on the prevalence of autism (ASD): the Developmental Disabilities and Autism Monitoring Network and the California Department of Developmental Services (CDDS), Department of Education's (IDEA) Individuals with Disabilities Education Act (IDEA) in California from 1931 to 2014, subsequently comparing the data at the national level also. The authors conclude as follows:

(i) The CDDS dataset suggests that prevalence has increased by a factor of 25 from the year of birth 1970–2012 and by as much as a factor of 1000 from the year of birth 1931–2012. (ii) CDDS continues to exclude most milder cases of autism, despite two different changes in its diagnostic criteria in the last decade. As a result, IDEA autism prevalence in California is substantially higher than CDDS prevalence (…) (Nevison et al., 2018, p. 4115).

A new report from the Commissioner for the Autism Society of the San Francisco Bay Area, based on data from the California Department of Developmental Disabilities in 2020 (Irva Hertz-Picciotto et al., 2020), states that the autism ratio in California in 7 years, from 2013 to 2020, had increased by about 13.6 % per year, amounting to a total increase in cases similar to the 33-year increase from 1980 to 2013. As is the case in California, autism ratios have experienced a significant increase in New Jersey; according to CDC data, its autism rate statewide was 1 in 32 eight year olds versus the rate at country level (USA) of 1 in 54 eight year olds. Tracking autism rates globally is difficult because many nations do not track, nor report, their autism rates, because there are no specific criteria for assessing autism, standardized for all nations, and because many countries of the world do not have the resources to conduct these assessments. Despite this, in 2021 the Global Health Data Exchange compiled autism rates for all countries in the world per 10,000 persons of any age (Global Health Data Exchange, 2021). The countries with the lowest rates of autism were the developed countries of Europe, with France having the lowest rate in the world, 1 in 144 persons. In contrast, the country with the highest autism rate in the world was Qatar with 151.20 cases per 10,000 children and 1 in 66 persons.

In view of the above, the purpose of the present research is to carry out a review of endocrine disruptors and neurodevelopmental disorders, focusing on four of the most studied pollutants to which pregnant women and children are exposed, such as polychlorinated biphenyls (PCBs), polybrominated diphenyl ethers (PBDEs), bisphenol A (BPA), and pesticides, analyzing their effect on the molecular mechanism of maternal and infant thyroid function essential for infant neurodevelopment and whose alteration has been associated with different neurodevelopmental disorders. To address this issue, the following research questions were formulated: (1) How does maternal and infant thyroid function affect neurodevelopment? (2) How does altered thyroid function contribute to neurodevelopmental disorders? (3) How do endocrine disruptors modify thyroid function and thus possibly promote neurodevelopmental disorders? (4) How do pesticides disrupt thyroid function and possibly increase neurodevelopmental disorders? This study contributes to the research, as it helps to understand the role played by environmental factors in the pathogenesis of neurodevelopmental disorders and autism, allowing the establishment of prevention and intervention strategies.

The remainder of the paper is organized as follows: In Section 2, we describe the methods. The results are presented in Section 3, followed by a discussion and the conclusions in 4 Discussion, 5 Conclusions, respectively.