A study published yesterday in the journal Environmental Health Perspectives, found that women with blood PCB levels which were in the top 25% of the range found in all individuals in the study, had double the chance of a failed embryo implantation, when compared with those in the quartile with the lowest blood PCB concentrations. In addition, the individuals in the upper 25% also had less success in conceiving a child after implantation, with a surprisingly reduced chance of success at just 41%. Thus, within that band the women were suffering very significantly lower odds of their in-vitro fertilization ultimately resulting in the birth of a child.
To provide a little bit of history here, PCBs were banned in the 1970s after much controversy, due to the realisation that they were persistent in the environment. When first used it was not known that chemicals like PCB, would also be concentrated by being eaten as nutrients in food and become more concentrated as passed up the animal food chain.
As a result PCBs in small (a few parts per million concentrations) quantities are still in the world’s environment having been spread universally around the oceans of the world. All humans now unavoidably exposed to them through contaminated food, primarily fish, but also meat and dairy.
It is this source which gives rise to the blood PCB levels witnessed by this study in those women participating. This news is going to give concern to many couples undergoing IVF treatment. This apparent almost doubling of the odds of implantation failure, is going to be hard for anyone to ignore. However, the researchers point out that there are likely to be many factors involved in implantation success, this chemical exposure may be one of them, but others may be present and more studies should be carried out to confirm these findings.
At this point the obvious question is to ask how comparable the PCBs levels measured in the women studied are with an average woman from the full population. The researchers point out that the women studied weren’t likely to differ much from normal urban populations. They were not from areas were the population is known to experience high PCB pollutant loadings.
Such high PCB risk populations are the Eskimos (Inuits), and those living in fishing villages which have a diet almost solely of high PCB fish. In addition, in recent years, there have been one-off PCB incidents affecting some populations. However, the women in the study were not from any such incidents. Many will have read, for example, of Taiwanese women suffering from contaminated cooking oil exposure, when some PCB drums were mistakenly used for cooking.
It may also be the case that this report, compiled from necessarily quite old data, provides a conclusion which over-emphasises the current problem. This may be the reality, given that PCB levels in the population as a whole are experiencing a decline, and therefore the study measurements may no longer be representative, with women today already receiving a lower burden of this contaminant than those in the study group.
Contamination gets into our blood primarily through low levels of PCB absorbed, mostly from eating fish, but also arising from meat and dairy sources. The new study has interesting findings not seen so clearly in studies conducted elsewhere. By Looking at IVF program patients the researchers were able to obtain data of good quality, and use data from individuals which were being monitored closely
It was pointed out that in the normal population experiencing normal pregnancies, the elevated conception failure rate would not be seen as it would simply be hidden as an undetected pregnancy.”
“PCBs in the environment and in humans are gradually declining”
The Environmental Protection Agency (EPA) outlawed the manufacture of PCBs in 1977, and PCBs are no longer manufactured nor are they allowed to be used in the United States, and many other nations. As a result of the ban, PCB levels in the environment are gradually reducing, and will continue to do so.