The latest MINE 391 assignment is a one pager regarding metal poisoning. In this Mining & The Environment class with Marcello Veiga we have learned about many important case studies on this topic; some of them natural and others human-induced. For this assignment we had to dig up something we hadn't learned about. Unfortunately there are too many examples of metal poisoning in the world, and I chose to write about an enormous arsenic poisoning problem in the Chinese province of Inner Mongolia. Here you go:
Arsenic Poisoning
Arsenic typically reaches humans through ingestion pathways of food or drinking water. It is a chronic illness and kills by affecting essential metabolic enzymes, leading to multiple organ failure. The Canadian interim maximum allowable concentration is 25 µg/L while the WHO guideline is 10 µg/L. As(III) is more toxic than As(V), and compounds of arsenic are much more toxic than the metal in its pure form. The first symptoms of arsenic poisoning are melanosis on the chest, back, limbs, and gums. Advanced symptoms include skin eruptions on hands, feet and torso that eventually lead to skin cancers. Other resultant health effects are anemia, gangrene, and cancer of the kidneys or bladder.
Huhhut Alluvial Basin of Inner Mongolia
The Huhhut Alluvial Basin of Inner Mongolia in northern China has been providing groundwater to inhabitants for decades for both domestic and agricultural use. This basin lies along the northern side of the Yellow River and south of the Daqing (Great Green) Mountains. It measures 4800 square kilometers and contains a 1500 meter thick aquifer made of poorly consolidated sediments from the Quaternary age that naturally contain high levels of arsenic (mainly As3+). No industrial or agricultural activities in the area contribute arsenic to the environment. No elevated levels of arsenic have been found in surface soil, fish, air, or crops.
Researchers concluded the aquifer creates a reducing environment high in organic material allowing for the relative ease of arsenic movement and accumulation. Water was previously tapped from shallow (less than 10 meter deep) dug wells, but they’ve been replaced by tubewells extracting from medium depth (less than 30 meters deep) or by deep artesian wells greater than 100 meters depth. Arsenic concentrations in the medium wells were found to be between 1 and 1500 µg/L, while deep wells ranged from 1 to 300 µg/L. Even the shallow wells contained high concentrations everywhere except around the margins of the basin.
Implications and Health Problems
National water studies had been conducted in 1984 and demonstrated the high level of arsenic, but no diagnoses had been made. In 1990 the problems first became apparent; skin lesions (melanosis, keratosis) and increased cancer rates. About 1500 arsenicosis cases existed by the mid 1990s. The affected region supports a population of over one million people -- 300,000 of which are believed to be drinking water containing arsenic in concentrations above the Chinese legal limit of 50 µg/L.
Solutions
Some areas have been provided low-arsenic surface water by pipes, or small-scale reverse osmosis facilities. Only a fraction of the affected area has been helped. This arsenic contamination problem is unique in that it affects both shallow water dug wells and groundwater piped wells, otherwise a solution would be much easier and cost effective. Surface water collection could be an option, but annual precipitation levels are not very high so it may not be feasible; there also exists the possibility of pathogens. No option exists to switch aquifers, so treatment of groundwater is necessary using arsenic removal technology. For a solution to work it must be cheap, easy to make, simple to use and maintain, and most importantly have the support of the local people. One affordable method is the zero-valent iron method used by MIT in 2004 in Nepal and in the 3-Kolshi filter in Bangladesh. Both use cheap and locally available materials. Unfortunately some technologies do not work well for As(III) removal so pre-treatment may be necessary to oxidize As(III) to As(V). Post treatment may also be required to remove bacteria.
Conclusion
The Chinese government failed to act when high levels were first discovered, and this has led to a serious humanitarian issue in the region. The distribution and speciation of arsenic in this area is especially problematic due to the prevalence of the more toxic and more difficult to treat species As(III) present at all depths of this vast aquifer. This problem is not limited to the Huhhut Alluvial Basin, but affects an enormous area of alluvial plains in northern China providing the drinking water for 5.6 million people. There were around 20,000 diagnosed cases of arsenicosis in the entire region as of 2001. Global arsenic poisoning is affecting millions, in Bangladesh, Cambodia, Vietnam, Nepal, and even New Zealand and the USA. As the MIT researchers and people like Marcello Veiga have proven, simple effective solutions can be found to prevent metal poisoning. The problematic areas must first be identified, and then the local people must be provided with solutions that they are capable and willing to adopt. It is through this process of identification and customized problem solving that millions of people can be spared such dreadful and unnecessary suffering.
References
Environment and Social Unit. World Bank. “Towards a More Effective Operational Response”. Jan 2004. 11 Mar. 2007.
Z. Luo et al. "Chronic arsenicism and skin cancer in Inner Mongolia -Consequences of arsenic in well water". SEGH Meeting Presentation, San Diego, CA June, 1995.
Wikipedia. "Arsenic Poisoning." 11 Mar. 2007 .
Clayton, Mark. "A Race to Fix a 30-Year-Old 'Solution'" Christian Science Monitor. 17 Feb. 2005. 11 Mar. 2007 .
Veiga, Marcello. “Chapter 05 - Fate of Metals in the Environment and Toxicity”. MINE 391 Notes. 2007.