An item which I had been researching is proving annoying. While it is clear pollution by plastics is obviously detrimental to our environment, it is difficult to determine the actual impact plastics are having on ecosystems and human health issues.
I was searching for something simple and quantitative, such as eating X number of plastic-packed meals cooked in a microwave oven would raise the risk of some disease by Y due to Z quantities of some plastic compound. But the reality is such conclusive data is not available for most plastic-related chemicals. Hence the determination of a causal link between general plastic pollution and human health is often difficult, unless there is a clear link between a particular type of plastic and detectable human ailments. One such example is Bisphenol-A (BPA) documented in a previous column (Banana leaf, plastic and other musings).
To understand the problem I am having, it may be helpful to understand how such research is conducted and why the available data is generally so poor.
Research into potentially toxic compounds such as plastics are usually done either as “cross-sectional studies” or “longitudinal studies”. A cross-sectional study looks at the effects and toxicity of a compound at some fixed point in time, usually after a significant number of people were found to have developed some unusual condition.
A longitudinal study would investigate and sample periodically the incidence of various conditions over a longer period. These conditions would have arisen from ingestion, inhalation, or skin contact with various compounds over time. The data is then analysed to establish significant correlations/causal links between the compounds and conditions.
It would also be fair to add that a cross-sectional study would likely have a target set of compounds in mind to investigate from the outset whereas a longitudinal study can begin with no pre-conceived ideas of any specific problematic compounds – the linkages would be established over time with the recorded cumulative consumption levels of various compounds.
And often a good piece of research combines both cross-sectional and longitudinal studies to offer a more compelling case for the findings.Cross-Sectional Study Example“Popcorn lung” is a serious lung disease linked to a chemical called diacetyl, which was used to give microwaveable bags of popcorn a buttery flavour and aroma. This condition was detected among workers in microwave popcorn manufacturing plants who were exposed to diacetyl for long periods of time, resulting in the deaths of many workers. Laboratory studies had already showed diacetyl causes severe epithelial damage in the nasal passages and pulmonary airways of rats.
Of course, such factories also use many other compounds in its production lines, but the problem chemical was quickly confirmed as diacetyl by lung tests called “forced expiratory volume in 1 second” (FEV1). People who worked in close and/or prolonged proximity with diacetyl had much poorer FEV1 results than people who had less or zero contact with the compound.
Such convincing evidence led to the eventual removal of diacetyl from microwave popcorn in 2007 by all USA manufacturers.
The problems with microwave popcorn did not end with diacetyl. Another more difficult problem linked with microwaveable popcorn was with the lining of the bags, which contained perfluorinated compounds (PFCs) to prevent grease seeping through the bags when the contents were heated in the microwave. PFCs were also used in pizza boxes, sandwich wrappers and non-stick frying pans. PFCs are part of a large, complex, and ever-growing class of synthetic chemicals known as PFAS (perfluoroalkyl and polyfluoroalkyl substances) which are widely used in the manufacture of many types of everyday products.
Such compounds are so prevalent and widespread that 98% of Americans have detectable amounts of PFAS in their blood. With such an extraordinarily high prevalence in the human population, it was very difficult to link any disease or condition directly to PFAS. Hence, the determination of the negative health impacts required a lengthy longitudinal study on PFAS and related compounds.
One such longitudinal study looked at the human population in an area in West Virginia, USA, where PFCs from a local factory had been contaminating the environment since the 1950s. Health data from 2005-2006 were followed up between 2008-2011 and covered 32,507 individuals. Interest was eventually focused on two chemicals called perfluorooctane sulfonate (PFOS) and perfluorooctanoic acid (PFOA) which result when PFCs are processed or broken down.
The longitudinal research data indicated that PFCs (and especially the derivatives PFOS and PFOA) were very likely responsible for unusually high incidences of kidney cancer, testicular cancer, ulcerative colitis, thyroid disease, hypercholesterolemia, and pregnancy-induced hypertension. These findings were corroborated in laboratory animal studies where it was also established that the biological impact of both PFOS and PFOA was practically identical.
As a result of this longitudinal study and others like it, PFOS was banned by the EU in 2011 and the USA banned PFOA and several other PFCs in 2016. For more information, please read this past article: Non-stick: C8 – cool name, not so cool stuff.
Not Acutely Toxic
A problem may be that many chemicals such as PFOA and PFOS are officially classified as “not acutely toxic for humans”. This is due to quirks in the classification of toxicity which was designed originally for the chemical industry rather than as an environmental risk factor. As such, many compounds are not considered dangerous or acutely toxic because they are not likely to provoke a serious biological reaction or death within a short period after exposure.
The same is true for plastic pollutants.
However, it does not mean there are no adverse health effects when environmental plastic pollutants are bio-accumulated in the body over a lengthy period. Importantly, there is often little data about any additional impacts on infants and younger humans.
Even worse, the effects of combining various pollutants are not charted in any detail even though studies on animals have shown that cumulative exposures to mixtures of pollutant chemicals can have exponential additive effects and increase the onset of adverse health/biological effects. The combinatory effect on humans is seldom studied; eg, a compound may not have any significant detrimental effect until it is combined with another chemical pollutant.
Plastics
This is a list of the most common plastics found dispersed in our environment:
- high-density polyethylene
- low-density polyethylene
- polyethylene terephthalate
- polypropylene
- polystyrene
- polyvinyl chloride (PVC)
These plastics are so prevalent and widespread that billions of people are either ingesting bits of them with their food or water, and/or breathing in particles of them every day.
That means an unknown (but probably huge) number of people are ingesting invisible chemicals which may be banned now but were present in older plastics, such as BPA. The long-term toxicity of BPA is well-established by now, but that is only one chemical out of very many.
It was not easy to establish causal links between many chemicals and their impacts on human health. The widespread presence of many chemicals in humans often preclude targeted cross-sectional studies on many common physical and mental health syndromes. Often, there are also not enough people wholly unexposed to the chemicals to act as a control group.
Similarly, longitudinal studies are also extremely complicated due to the wide distribution and huge varieties of chemicals. Unless there are concentrations of specific compounds which can be eventually isolated to affect only particular populations, then it is often impossible to associate long-term chemical pollutant exposures with health issues.
Phthalates
One important group of plastic chemicals is called “phthalates”. There are no doubts that members of this group of chemicals causes male developmental toxicity in rats. The effect is so consistent it is known as “phthalate syndrome” in rats, which is characterised by severe developmental defects in the genitalia of male rats.
As phthalates are used to impart textures to common PVC products, there was enough concern that the US Consumer Product Safety Commission convened a Chronic Hazard Advisory Panel (CHAP) in 2008 to study the effects on children’s health of all phthalates and phthalate alternatives as used in children’s toys and child care articles. The outcome was a very interesting 597-page report published in July 2014.
Due to unethical/dangerous issues involved in dosing infants with phthalates, the study had to rely heavily on studies on laboratory mammals, including mice, rats and a primate, marmosets. In some cases, human fetal material was grafted onto the experimental animals and the effects of various kinds of phthalates were observed. Although the outcomes were not directly conclusive due to several complicating factors, CHAP found enough evidence to maintain bans on dibutyl phthalate (DBP), butylbenzyl phthalate (BBP), and di(2-ethylhexyl) phthalate (DEHP) in toys and recommended further studies on these compounds in food and other products. Additionally, CHAP also applied a new interim ban on diisononyl phthalate (DINP) because this chemical was estimated to contribute to the cumulative risk of other phthalates.
As an investigative study on phthalates, the CHAP report was an impressive document. However, the study also frankly stated the scope of its investigation was limited to phthalates. There was no attempt to assess cumulative health impacts when phthalates were combined, for example, with BPA.
And to be honest, such a scope would be too wide and complex to cover the huge range of pervasive chemical pollutants in our environment. However, one must understand that any chemicals which are banned now would have been permitted earlier, and these old compounds are mostly still around, polluting our food and air. These chemicals by themselves, or in combination with other pollutants, are almost certainly slow-acting toxins affecting our physical and mental health in ways we do not fully understand yet.
The views expressed are entirely the writer’s own.
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