Thursday, December 10, 2009

Heavy Metals: Alarming Results

Guiyu, a region in the Chinese province of Guangdong, together with New Delhi in India, is one of the most popular destinations for e-waste [1,2]. Within 52 squared kilometers, Guiyu alone has been estimated to accommodate millions of tonnes of domestic and overseas e-waste per year [3]. Several studies have detected soaring levels of toxic heavy metals in Guiyu, in samples of dust, soil, river sediment, surface water, and groundwater [1,2,4,5,6,7]. Levels well above Canadian environmental standards.

In a previous post I outlined the human health risks of exposure to lead, mercury, and cadmium. At the end of each description I provided a threshold or guidance value set out by the Canadian government, which essentially is the exposure value deemed to be "safe" based on past research. In my literature review I came across a number of studies looking at these particularly toxic heavy metals, and describing the exposure levels among residents of communities where e-waste disassembly is occurring. I found the results of these studies astounding! And you will eventually come to understand why, after reading this post. Given the extensive amount of research that already describes the human health impacts of exposure to these metals, a lot of the studies did not measure health outcomes (i.e. cancer, behavioural changes, kidney damage, etc.). The studies I chose to look at were those that measured internal exposure (human hair, blood, umbilical cord blood and meconium samples).

Lead Exposure
I came across four studies measuring blood lead levels in children, and one study looking at blood lead levels in adults. Unfortunately, one of the studies in children [8], as well as the study of adult exposure [9], could not be retrieved due to a lack of availability. I attempted to retrieve the articles from the main authors but was unsuccessful. In addition, I also found two studies that measured lead content in hair samples. One was conducted in China[10] and the other was conducted in India (one of the very few published studies I looked at that was not conducted in China)[11]. Human scalp hair is a convenient and less invasive biological measure that can reflect long-term lead exposure. However, for this posting I decided to focus on the three studies that looked at blood lead levels, since blood samples are the most commonly used, and also deemed to be the most accurate assessment of human lead exposure [10,12].

I have created and included a table outlining the blood lead levels in the three studies that measured it. As you look at the levels reported, recall what was mentioned in my previously posting about lead: no lead exposure levels are deemed safe in children, and the current Canadian threshold for treatment is 10 micrograms per decilitre in blood.

Click to enlarge!
As is apparent in the table, blood lead levels were strikingly high in the study populations observed overall, but even more so in the children living in Guiyu, where e-wastes are handled. In the Li et al. study, neonatal exposure to lead was highly correlated with parental activities in e-waste recycling. Lead content in meconium was an important measure in this study as it is believed to reflect the accumulation of lead during pregnancy when mothers have elevated levels of lead circulating in their blood [13]. This was important because maternal blood lead levels were not measured. With regards to the two other studies (Huo et al. & Zheng et al.), the control group participants were selected from the same region, Chendian, and essentially the same study design was used, only the studies were conducted two years apart (2004 versus 2006, respectively). In both studies, residence in Guiyu was a risk factor for elevated blood lead levels. In the later study, Zheng et al., additional risk factors were identified: paternal employment in e-waste recycling (OR=4.61; p=0.003), amount of time spent playing outside near the road everyday (OR=1.73; p=0.02), frequency that the child would suck their fingers (OR=2.85; p=0.009), and age (OR=1.72; p=0.033). Even though the study participants in both studies were different, they came from the same population; therefore, it is interesting to compare the mean lead levels and percent of participants with lead levels above 10 micrograms per decilitre in each study. It appears that the blood lead levels are decreasing, although I'm not sure whether this difference is statistically significant. The Chinese government has implemented control measures to reduce pollution produced from primitive e-waste recycling. Such measures include stricter control of the importation of e-waste, and health education campaigns about the dangers and means of preventing lead poisoning [14,15].

Mercury & Cadmium Exposure
In my next post I'll continue to unveil the results from studies on mercury and cadmium exposure.



4 comments:

  1. Might retitle Lead given the focus….
    Yes, alarming. I really appreciate the table, good way of focusing on one area with intensive investigation. What kinds of matching were carried out between the exposed and control or referent groups? [as I see that results were not controlled for age [important] and gender [maybe less so]) Good to have the variety of exposure-related factors i.e. location, activity, behaviour. Glad some steps are being taken to reduce exposures - Can you link the timing of the declines with introduction of measures, or given the challenges cited in one of the papers, do you think effectiveness is an issue?

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  3. EnvironmentCare.in(http://www.environmentcare.in/) is India's 1st environmental B2B portal.It is an online one stop go Green source to provide end to end solutions for environment protection, pollution control management, energy conservation, renewable energy, e-waste management and safety management.
    EnvironmentCare.in also provide Green News, live discussion, Blogs, Environment friendly calculator, Games with Learn and much more interesting and educational section.

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  4. Thanks for sharing the valuable information,This is useful information for online learners.
    electronic e waste and recycling

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