Since Volkswagen, the world’s largest automobile manufacturer, admitted that it misled U.S. regulators in exhaust emissions tests, repercussions continue to be extensive.

The BBC News(link is external) now reports that Switzerland has temporarily banned the sale of Volkswagen diesel-engine models which could be connected with the emission tests scandal, while concerns are now being raised that other car makers may be implicated.

Another possible allegation, given that rapidly rising rates of autism in recent years are linked with diesel vehicle emissions, is that the automobile industry might be a factor.

Diesel exhaust is mainly composed of gas and particles, while both contribute to health risks, the size of diesel particulates causing greatest health concerns are ‘fine,’ and ‘ultra-fine,’ as these can avoid human respiratory defences, depositing deep inside lungs.

A study just published entitled, “Autism Spectrum Disorder and particulate matter air pollution before, during, and after pregnancy: A nested case–control analysis within the Nurses’ Health Study II cohort,” found that higher maternal exposure to the kind of pollution associated with diesel car engines, during pregnancy, was associated with a greater likelihood of a child later developing autism.

The authors of the current study point out that several previous investigations have also found associations of air pollution with autism. These studies suggest increased chances of having a child with Autistic Spectrum Disorder following higher exposures to diesel particulate matter, as well as proximity to a freeway.

The current study, published in the academic journal, Environmental Health Perspectives, involved investigating 116,430 U.S. women. For each child born, estimated exposures to particulate matter, before, during and after pregnancy, were calculated by averaging monthly concentrations for the mother’s residential address during the relevant months.

The authors argued the association of particulate matter exposure to pregnancy, which they found, is consistent with Autistic Spectrum Disorder being caused before birth, as has already suggested by prior research. Exposure to high levels of environmental toxins when the foetus is in the uterus might interfere with normal processes of brain development.

Autism impacts on social interaction, communication, interests and behaviour. Autism Spectrum Disorder includes Asperger syndrome and childhood autism; the main features typically start to develop in childhood.

One in 68 children in the United States have now been identified with an Autism Spectrum Disorder, according to the latest Centers for Disease Control and Prevention numbers released in 2014, an estimate which is roughly 30 percent higher than the CDC’s previous measure, released in 2012, which found autism rates of 1 in 88 children.

Another recent study, the first to examine the association between air pollution and autism across the United States, and entitled, “Perinatal exposure to air pollutants and autism spectrum disorder in the children of the Nurses’ Health Study II,” implicated diesel.

The research found that women exposed to the highest 20% levels of diesel pollution, including diesel, lead, manganese, and cadmium, versus the lowest 20% of diesel, and these other hazardous air pollutant levels, were twice as likely to have a child with Autism Spectrum Disorder.

Published in the academic journal Environmental Health Perspectives, the study pointed out that the metals which were investigated, and traffic-related pollution (e.g., diesel), are known to be neurotoxicants, inducing inflammatory responses in humans and animals—processes that have been implicated in autism.

Another recent study entitled, “Prenatal and early life exposure to high-level diesel exhaust particles leads to increased locomotor activity and repetitive behaviors in mice,” was also inspired by recent research reporting a link between increased incidence of autism, and living closely to major highways, suggesting a possible role for pollutants from highway traffic.

The study published in the journal Autism Research, exposed female mice and their offspring to diesel exhaust particles during pregnancy and nursing.  Compared to the other mice, diesel exhaust particles-exposed offspring, exhibited increased behaviours which may be linked to the restricted and repetitive actions seen in autism patients.

Once diesel exhaust particles have entered the blood-stream, ultra fine particles can also be transported to other organs. Does this explain recent research findings such as a 373 percent increase in the number of reported cases of autism spectrum disorders from 1980 to 1994 in California?

A study entitled, “Trends in diagnosis rates for autism and ADHD at hospital discharge in the context of other psychiatric diagnoses,” analyzed discharges from 1989 to 2000 in U.S. community hospitals.

The study, published in the journal Psychiatric Services, concludes there was a 358 percent increase in autism prevalence during this period. The authors believe this represents a genuine increase, not just better detection, and one explanation is an increase in exposure to environmental toxins.

A second possibility relates to the recent increasing survival rate of low birth-weight and otherwise compromised babies, at elevated risk of future developmental disorders. However, the authors contend it is unlikely that the increase in the number of low birth-weight babies alone could account for such a large upsurge in rates of developmental disorders.

A recent review of studies in experimental animals of exposure to diesel exhaust just before and after birth, entitled “Developmental toxicity of diesel exhaust: A review of studies in experimental animals,” reveals changes in growth, sexual development, hormone levels, sperm counts, behaviour, neurotransmitters, cell pathology of the testes and brain as well as susceptibility to allergies, in rodent offspring.

The study, published in the academic journal, Reproductive Toxicology, points out that diesel exhaust contains more than one hundred different organic and inorganic compounds, and diesel exhaust particles are usually the most common combustion-derived nano particles and environmental particulate pollution, in urban environmental air.

Cynthia Nevison from the Institute for Arctic and Alpine Research, University of Colorado, recently published an investigation entitled “A comparison of temporal trends in United States autism prevalence to trends in suspected environmental factors,” where she points out that road traffic pollution, given the evidence that it’s been currently improving, might not explain rising rates of autism.

Her study, published in the journal, Environmental Health, contends that a recent large drop in vehicular emissions occurred mainly by the 1980s, because of the introduction of catalytic converters in the 1970s, as well as ongoing improvements in fuel and emissions technology.

Emissions of black carbon, which are closely associated with diesel fuel combustion and large trucks, also appear to be dropping significantly, thanks to developments such as diesel particle filters.

She points out that recent findings of autism associated with particulates exposure during pregnancy as well as with birth residence proximity to freeways, but not major roads, might suggest a connection to large diesel trucks, which travel more often on freeways than surface streets.

This may also implicate ultra fine or nano particles, whose concentration is high near freeway traffic, but falls off exponentially away from the freeway, partly due to atmospheric dilution. Nevison also cites evidence that large diesel truck miles travelled have increased four-fold from 1970 to 2005, but the increase in miles appears to be overwhelmed by larger reductions in emissions per mile for key pollutants.

However, she also contends that a counter trend toward increasing emissions of nano particles, cannot be ruled out.

Europe has embraced diesel cars to a much greater extent than the USA, so higher rates of autism might be expected, if diesel pollution was a key variable.

Yet, according to a study entitled, “Prevalence and incidence rates of autism in the U.K.: time trend from 2004–2010,” the estimated prevalence rates of autism in the U.K. population for one comparison year 2008, was about 4 per 1000 in 8-year-old boys, far lower than 11 per 1000 in 8-year-old boys reported by the CDC from the USA, for the same calendar year.

But, according to the study which cites this data, published in the journal BMJ Open, such large differences between these two countries are similar to contrasts in rates reported for attention deficit hyperactivity disorder in the U.K. and the U.S., so these differences may reflect something to do with diagnostic practice in childhood generally.

A study entitled “Air pollution exposure during pregnancy and childhood autistic traits in four European population-based cohort studies: The ESCAPE Project,” found that exposure to nitrous dioxide and particulate matter before birth was not associated with later autistic traits in children from four to ten years of age, in four European population-based studies.

The authors of this investigation, published in Environmental Health Perspectives and involving 8,079 children from Sweden, The Netherlands, Italy and Spain, point out that prenatal exposure to air pollution could be related to the more narrowly defined Autism Spectrum Disorder, but not with broader autistic traits in children, as measured in this research.

While the controversy is far from over, possible links with currently dramatically rising rates of autism, indicate that proper measurement of diesel emissions is a serious matter, and not to be trucked with.

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