Sunday, December 13, 2009

Dioxins and Furans: Not in our backyard, yet?

Persistent Organic Pollutants: How did they get there?!
In an earlier post I wrote about polybrominated diphenyl ethers (PBDEs), which are among the list of chemical substances that are classified as persistent organic pollutants (POPs). POPs are chemicals that have three main characteristics: 1) they are stable compounds, enabling them to persist in the environment; 2) they are lipid (fat) soluble, which combined with their stability, enables them to accumulate up the food chain; 3) they have the ability to act as endocrine (hormone) disruptors [1]. New studies continue to discover the presence of POPs in environments where they have never been produced or even used before, indicating their ability to be transported over long-ranges. These characteristics, along with the increasing evidence of adverse health outcomes associated with exposure, have sparked international discussion about the need to urgently reduce and eliminate the production of these chemicals [2].

Dioxins and Furans: Source and Health Impacts

Polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) are another type of POPs that were studied in the e-waste literature I reviewed. There is a recurrent theme in my postings about the dangers associated with primitive e-waste recycling techniques used in poorer countries where a vast majority of the world's e-waste is processed. In the case of PCDD/Fs, their affiliation with e-waste depends on these crude recycling processes. Plastics made from polyvinyl chloride (26% of the plastic found in e-waste by volume), once processed through uncontrolled open burning, can generate PCDD/Fs [3].

Dioxins and furans can enter the body via inhalation, ingestion and skin absorption. Exposure to PCDD/Fs at high levels can lead to chloracne (severe skin disease), darkening of the skin, and altered liver function. Long-term exposure can lead to damage of the immune, nervous and endocrine systems and impaired reproductive function [3,5]. Specifically, dioxins are classified as Group 1 "known human carcinogens" according to the World Health Organization's (WHO) International Agency for Research on Cancer [4]. These carcinogenic effects have only been observed with high dose exposures; there is insufficient evidence to prove that low-level exposure to dioxins and furans can cause cancer [5].

The Tolerable Monthly Intake for dioxins and furans is 70 picograms per kilogram of body weight (pg/kg), as outlined by the WHO. This is the amount that can be ingested per month over a lifetime without inducing substantial health risk [5].

What's been reported in the E-waste literature?
A number of studies have quantified the level of PCDD/Fs in air, soil, dust, sediment, freshwater, fish, and cow milk samples, in a number of regions where e-waste recycling has taken place [6]. My interests lied in those studies that quantified human internal exposure to these hazardous agents, using biological markers such as human breast milk, placenta, hair, blood and urine. I did review one study that estimated daily human exposure using many environmental samples (soil, dust, and surface samples). This study was an interesting starting point for my research in this area because I kept these estimates in mind when looking at the studies that measured internal exposure using biological markers. The estimated daily intake of PCDD/Fs via soil/dust ingestion and dermal exposure, according to this study, was two times higher for people who are exposed to e-waste recycling facilities in Taizhou (2.3 and 0.363 pg/kg/day for children and adults, respectively), compared to people who are exposed to chemical industrial sites (0.021 and 0.0053 pg/kg/day for children and adults, respectively) in various areas also in Eastern China [7]. Note that these estimates did not include a number of other sources of PCDD/Fs exposure such as through food, water, breast milk etc.

From here I turned to another study that was a health risk assessment (systematic calculation of risk) of dioxins and furans, using samples of human milk, placenta and hair from residents also in the Taizhou region*. The 10 study participants were all women of child-bearing age who had been either exposed to e-waste recycling activities as residents in Taizhou, or
unexposed residents in a neighbouring city (245 km away from Taizhou) for at least two years, and who had given birth at either of two study sites between August and December 2005. Each biological sample provided a different picture of the overall exposure. PCDD/Fs in hair samples indicated accumulation and atmospheric deposition on the hair surface; consequently, it is difficult to distinguish between internal and external contamination [8]. Analysis of the placenta is a good indication of prenatal exposure, and breast milk samples reflects maternal body burden and the postnatal transfer of PCDD/Fs to infants [9].

The results showed that there were significantly different PCDD/F concentrations in the placenta and hair samples after comparing the exposed group to the unexposed group. The total concentrations found in breast milk samples from the exposed group were two times higher than the unexposed group, but this difference was not found to be statistically significant (p>0.05). Background pollution, dietary habits and personal characteristics were all important factors influencing the total concentrations of PCDD/Fs [
9]. All human milk samples from the Taizhou group, and 80% of the samples taken from the women in the reference group, exceeded the European Union's maximum permitted levels in milk (3 pg WHO-TEQ/g lipid) [10]. The health risk assessment for infants estimated that the daily intake of PCDD/Fs via breast milk was 102.98 +/- 67.65 pg TEQ/kg body weight/day in the exposed group and 45.83 +/- 36.22 pg TEQ/kg body weight/day in the unexposed. Both of these values exceed the WHO tolerable daily intake (1-4 pg TEQ/kg body weight/day) [11]. High intake exceeding the toxicological limit during breast feeding is concerning because of the long length of time that it takes for the toxins to be removed from the body (7 to 12 years), faster and greater absorption in infants and children, and the immature body defenses in infants [9].

A third study was found that measured PCDD/F concentrations in hair samples from 64 randomly selected male workers at e-waste factories in eastern China. The study did not have it's own comparison group, and was therefore not looked at in great detail. The results from this study similarly found vastly greater concentrations of PCDD/Fs in hair samples analyzed compared to other known contaminated areas, and compared to the concentrations found in healthy study participants in Japan [12].

Tying things together
At the beginning of this post I mentioned that one of the properties of POPs is that they can travel over long distances. I was kind of surprised to have never really found a comprehensive article reviewing whose health is being affected by e-waste (big and small, currently or in the future). I read a bunch of media articles and blog posts talking about how as North Americans, we don't really experience the major effects of the international shipment and mismanagement of e-waste. I think this is a huge misconception, because we are all impacted by e-waste, even if we aren't the ones working in the family-owned workshops. If not in the present, then most likely in the future, we will all be impacted by e-waste if innovative and stricter policies aren't implemented.

Hopefully this is motivation for those decision makers that aren't motivated by the devastating results presented above, and in previous posts, about the human health impacts already occurring.


* Taizhou has become one of the main receivers of e-waste in China, in recent years. It receives an estimated 2.2 million tonnes of e-waste on an annual basis, and the industry employs an estimated forty thousand people. Most of the recycling that takes place in this region involves open burning, acid baths, and manual disassembly of e-waste [9].

17 comments:

  1. Very important papers in this one, with pretty good estimates of body burden. Likely worth being clearer about the focus of the study e.g. exposure assessment +/- source apportionment, risk assessment, and the time frame e.g. x-sectional (most). I very much like your style conveying them. It might be good to have graphics as well.

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