New Delhi: Pregnant women exposed to high levels of diesel fumes and mercury are twice as likely to give birth to autistic children compared with those living in less polluted areas, according to a study published in Environmental Health Perspectives journal on Tuesday.

Autism is characterized by delays or abnormal functioning before the age of three years in social interaction and communication. It also leads to restricted, repetitive and stereotyped patterns of behaviour, interests and activities.

The research was conducted by Harvard University’s School of Public Health in the US.

“Perinatal exposures to the highest versus lowest quintile of diesel, lead, manganese, mercury, methylene chloride, and an overall measure of metals were significantly associated with ASD (autism spectrum disorder)," the researchers said in the study published in the peer-reviewed journal. “For most pollutants, associations were stronger for boys (279 cases) than girls (46 cases) and significantly different according to sex."

Though the causes of autism are poorly understood, environmental exposures during the gestation period in particular have been implicated as a reason.

The study adds to an increasing body of research linking health effects to environmental pollution.

There are studies which link diesel exhaust or particulate matter to cardiovascular diseases, asthma and even cancer in the long term, said Vivek Chattopadhyaya, programme manager, air pollution control unit at New Delhi-based Centre for Science and Environment, a non-proft organization. “In 2012, World Health Organization classified diesel exhaust as a class I carcinogen, keeping it on the same pedestal as cigarette smoking, thus proving its cancer causing capability."

WHO should take note of such studies and guide countries on air quality guidelines and air toxins accordingly, Chattopadhyaya said. “There is no special monitoring for diesel particulate matter in the country. We need to start doing that. We should draw policy messages from such studies and need a road map to control diesel emissions in the country," he said, adding that 60% of the passenger vehicles in the country run on diesel, in addition to all trucks and pickups.

Using data from the Nurses’ Health Study II, a long-term research that began in 1989 involving more than 116,000 nurses, the authors analysed 325 women with children affected by autism and 22,000 women who had children without autism.

“We observed significant positive linear trends between pollutant concentration and ASD for diesel particulate matter, lead, manganese, methylene chloride, mercury, and nickel. The positive trend for the pooled metals metric and ASD was highly significant and displayed the most regularly monotonic linear dose­response of all exposures examined. Additionally, of all pollutants in the dataset, the highest quintiles of diesel and mercury were most strongly associated with ASD, and unlike most pollutants examined, these were positively associated with ASD in both boys and girls," the study says.

“Over the years, research has by and large, established that peri and ante natal environmental exposure to toxins can hamper brain development. However, this needs to study this in greater detail with bigger sample size in different parts of the world," says Rajesh Sagar, associate professor of psychiatry, All India Institute of Medical Science.

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