Mothers-to-be who are exposed to toxic chemicals which have been banned for decades have smaller babies, a study shows.
Persistent organic pollutants (POPs) were outlawed in the 1970s after it was found they can cause cancer and damage the environment.
Despite efforts to eliminate all traces of the potent chemicals, POPs remain in the food chain today – mainly in dairy, meat and fish.
Researchers found women who were exposed to high levels of POPs in pregnancy went on to have smaller foetuses.
Babies had heads that measured up to 6.4mm (0.25in) smaller. Some also had a smaller stomach circumference and shorter thigh bones.
In pregnancy, the chemicals, which were widely used in manufacturing as far back as the 1930s, can transfer to the baby through the placenta.
Mothers-to-be who are exposed to toxic chemicals which have been banned for decades but are still found in the food chain have smaller babies, a study shows (stock)
The study, published in the journal JAMA Pediatrics, involved 2,284 women from the US between 2009 and 2013.
Researchers from the National Institutes of Health said although the effects of POPs on fetal size was small, it suggests even low amounts may be toxic.
Lead author Dr Pauline Mendola said: ‘Even at low levels, there is evidence of a possible effect on fetal growth.’
The women in the study gave blood samples early in their pregnancy, between eight and 13 weeks, which was analysed for the presence of 76 POPs.
This included dioxins and dioxin-like substances, including PCBs, which can travel long distances from the source of emission.
POPs become stronger in concentration as they move up the food chain, a process known as ‘biomagnification’, meaning predators at the top of the food chain consume the most POPs.
WHAT ARE PERSISTENT ORGANIC POLLUTANTS?
Persistent organic pollutants (POPs) are toxic chemicals that have negative health effects on humans, animals and the environment.
They persist for long periods of time and can accumulate in the environment and pass between different species through the food chain.
They can be transported by wind and water, so POPs generated in one country can transport to another.
They were widely used in industry following the World War II.
Many of the chemicals were beneficial for pest and disease control, crop production and industrial processes.
Some well known POPs include PCBs, DDT and dioxins.
DDT controls mosquitoes that carry malaria, but is also responsible for the thinning of egg shells of certain birds to the point where their offspring cannot live.
What are the dangers?
Animals exposed to POP are at risk of a decline in number, diseases or abnormalities, studies have shown. The link has been seen in a certain kinds of fish, birds and mammals.
In humans, even low levels of POPs can lead, among others, to increased cancer risk, reproductive disorders, alteration of the immune system, neurobehavioural impairment, endocrine disruption, genotoxicity – which may lead to cancer – and increased birth defects, according to the World Health Organization.
How are people exposed to POPs?
People are mainly exposed to POPs through contaminated foods. Less common exposure routes include drinking contaminated water and direct contact with the chemicals.
In people and other mammals alike, POPs can be transferred through the placenta and breast milk to developing offspring.
POPs work their way through the food chain by accumulating in the body fat of living organisms and becoming more concentrated as they move from one creature to another. This process is known as ‘biomagnification.’
When contaminants found in small amounts at the bottom of the food chain biomagnify, they can pose a significant hazard to organisms at the top of the food chain. This means that even small releases of POPs can have significant impacts.
Source: Environmental Protection Agency
The POP levels in each woman’s blood were listed as percentiles, with the highest levels set at 100 and the lowest at one.
The researchers then collected data on the size of the babies as they were growing between 16 and 40 weeks gestation.
Head circumference, abdominal circumference, and femur (thigh bone) length was measured by the sonographers at five appointments.
Scientists compared measurements of babies born to women in the 75th percentile of POP level to those of women in the 25th percentile.
In general, a higher exposure to a mixture of POPs tended to raise the risk of having a smaller baby.
When the POPs were broken down into individual chemicals, the scientists saw PCBs had a particularly bad effect.
High levels of PCBs, which are pesticides that are highly toxic to fish and can be passed to humans, were linked to foetuses having a head circumference around 6.4mm (0.25in) smaller, on average.
The foetuses’ abdominal circumference was around 2.4mm (0.09in) smaller, results revealed.
Another type of POP called OPs, used in mosquito insecticides, were linked to smaller heads, abdomens and femurs.
High levels of PBDEs – flame-retardant chemicals used in furniture, electronics and other consumer products – also affected growth.
It was linked to an average abdominal circumference reduction of 2.4mm (0.09in) and an average femur length reduction of 0.5mm (0.019in).
The researchers concluded that even if exposure to POPs were successfully reduced, their damaging effects can last decades longer.
World health leaders signed a global treaty in 2001 to eliminate the production of POPs entirely.
Initially 12 types of POPs, known as the ‘dirty twelve’, were listed as having serious effects on humans and the environment. A further 16 were added to the list.
Health risks include cancer, birth defects, dysfunctional immune and reproductive systems, greater susceptibility to disease and diminished intelligence.
The women’s POP levels were recorded as lower than those of pregnant women in a 2003-2004 cohort.
The researchers believe their findings may be conservative and might not reflect the risk for women with certain occupations or other high exposures to POPs, they said.
In a linked editorial published in the journal JAMA Pediatrics, a group of researchers not involved in the study said the study demonstrated low-level exposure ‘does matter.
‘The bottom line is that no chemical that persists in the environment should be introduced in the first place.
‘The legacy of these chemicals is often irreversible and has the potential to have deleterious implications for future generations.’