Arsenic Contamination of Ground water

Arsenic is highly toxic and carcinogenic. Groundwater is particularly vulnerable to contamination with arsenic as a result of natural geochemical processes and problems can be exacerbated by mining activity. Even natural concentrations of arsenic in groundwater can limit its suitability for drinking.

It is now apparent that arsenic contamination of groundwater is quite extensive. In the last eight years, BGS has undertaken a series of collaborative investigations into the arsenic contamination of groundwater in various countries.These investigations have included both 'mining-related' and 'natural' sources of arsenic contamination.


What is arsenic?

Arsenic is a semi-metal, a member of the nitrogen family. It occurs naturally in the earth and in the seas. It is odorless and tasteless. Arsenic is an element (As) that occurs in the earth’s crust-rock, soil, all natural sources of exposure, or can be traced to deep water brines used to produce oil and natural gas. Consumption of food and water are the major sources of arsenic exposure for the majority of US citizens. People may also be exposed from industrial sources, as arsenic is used in semiconductor manufacturing, petroleum refining, wood preservatives, animal feed additives, and herbicides.

Arsenic can combine with other elements to form inorganic and organic arsenicals. In general, inorganic derivatives are regarded as more toxic than the organic forms. While food contains both inorganic and organic arsenicals, primarily inorganic forms are present in water. Exposure to arsenic at high levels poses serious health effects as it is a known human carcinogen. In addition, it has been reported to affect the vascular system in humans and has been associated with the development of diabetes.

As compared to the Western part of the United States, it is relatively rare contaminant in Pennsylvania groundwater supplies. A recent survey by the U.S Geological Survey (USGS) found that arsenic exceeded 5 ppb in 5% of wells in Pennsylvania.


Measurement

On June 22, 2000 EPA proposed a 5 ppb standard for arsenic. EPA requested comment on 10 ppb, 5 ppb and 3 ppb. Based on the comments, EPA is implementing a 10 ppb standard for arsenic. This rule became effective on February 22, 2002 and systems must comply with the new 10 ppb standard is January 23, 2006.

Symptoms

Observable symptoms of arsenic poisoning are: thickening and discoloration of the skin, stomach pain, nausea, vomiting, diarrhea, numbness in hands and feet, partial paralysis, and blindness.


How does it comes in private water system

It is widely thought that naturally occurring arsenic dissolves out of certain rock formations when ground water levels drop significantly. Surface arsenic-related pollutants enter the ground water system by gradually moving with the flow of ground water from rains, melting of snow, etc. Either way, ongoing testing for arsenic is an important strategy by the private water system owner to safeguard the health and well being of their family.


Risk factor

Like many contaminants in drinking water, the element is potentially hazardous at levels or concentrations that do not impart a noticeable taste, odor, or appearance to the water. Your best course of action is to get you water tested and compile as much information as possible about your water supply source, well construction, surrounding land-use, and local geology. If you do have an arsenic problem, there are water treatment technologies available now that can reduce or even remove arsenic from your drinking water.


Remidial steps to make arsenic water into consuming water

The following water treatment technologies are effective in reducing arsenic from drinking water:

1.Activated alumina filters
2.Anion exchange
3.Distillation
4.Reverse Osmosis
5.Nanofiltration
6. Iron Oxide Filters

Pretreatment may be needed in some cases to ensure acceptable treatment by the primary unit. Also, as a safeguard against organic arsenic, granular activated carbon filtration should be added. Some of the treatment technologies may not be amenable to point-of-entry, whole house treatments. In these cases, point-of-use units may be the best option. Periodic testing should be maintained after the treatment system is in place to ensure objectives are being met.


Affecting River

 The pandemic arsenic pollution in the Bengal Basin is caused by superimposed effects of the preferential entrapment of As in organic-rich deltaic sediments during the early- to mid-Holocene, when the sea level rose; later, severe reducing conditions developed, causing the release of As into groundwater. None of these features characterize the Ganga Alluvial Plain, where sediments in the mega fans from the Himalayan rivers that cover major parts of the alluvial plain are sandy, and associated groundwater is not reduced to the level required to cause significant mobilization of As. Chakraborti et al. (2003) recently reported severe As pollution in moderately reducing groundwater in Semaria Ojha Patti, Bihar, located within a narrow entrenched floodplain over 300 km from the head of the Ganga delta. Such local conditions are not representative of the Ganga Alluvial Plain. It is scientifically unrealistic for Chakraborti et al. (2003) to extrapolate from such local occurrences that "groundwater will be arsenic contaminated over a wide region" in the well-populated Ganga Alluvial Plain.