Jovan Ahmed Nayeem, NSTU Correspondent.

A threat for society
Groundwater in Bangladesh, which is used as drinking water, is found to be contaminated with many heavy metals, including arsenic, lead, cadmium, chromium, copper, mercury, nickel, and uranium. Of these, arsenic has been determined to be the most significant health issue; with about 49% of the water being likely contaminated with concentrations above the WHO guidelines, affecting 35 to 77 million people within the country. Arsenic contamination of shallow groundwater is a natural occurring problem that has been further made worse by the use of tube wells, which extract groundwater. Since the 1970s, the government started instituting the use of shallow tube wells to avoid the consumption of surface water, which is often contaminated with various bacteria. These tube wells, however, reached the arsenic-contaminated groundwater. This issue is more prevalent in inland areas and rural areas, where 97% of the population uses tube wells. Health effects of consumption of arsenic-contaminated water include skin pigmentation changes and lesions, which could be a precursor to skin cancer. It can also cause lung and bladder consumption, as well as developmental effects, neurotoxicity, diabetes, pulmonary disease and cardiovascular disease.
In coastal areas, the heavy metal contamination has also had an effect in marine life and the local ecology. This, in turn, affects the economic output of the region that relies partly on aquaculture. For instance, high levels of metals may affect the reproductive capabilities of the native ecology or contaminate the fish. If the fish have too high levels of metals, a fisher may not be able to sell it for consumption. If a consumer eats fish with high levels of metal contamination, he is at risk for health issues, such as cancer, kidney failure, or various metal poisoning. There is also a possibility that fish will move further away from these areas, to avoid the toxic areas, which would also affect the livelihood of the fishermen in the area.
Causes of groundwater contamination
Causes of groundwater pollution include-
Naturally-occurring (geogenic)
On-site sanitation systems
Sewage and sewage sludge
Fertilizers and pesticides
Commercial and industrial leaks
Hydraulic fracturing
Landfill leachate
Effects of Contaminated Groundwater
Contaminated groundwater can lead to severe effects on the environment, animals, and human beings. Firstly, groundwater is the primary source of drinking water for most people and animals around the globe. Once the groundwater is contaminated with harmful chemicals and bacteria, the humans and animals consume the harmful substances through drinking water and subsequently suffer health problems such as amoeba, typhoid, diarrhea, and even cancer. Secondly, the trees and vegetation that rely on groundwater are likely to dry up after absorbing contaminated water. As a result, the loss of vegetation leads to an imbalance in the ecosystem. Thirdly, contaminated groundwater may seep into rivers and streams and lead to the loss of marine life which is detrimental to the environment. Lastly, when groundwater is contaminated with reactive substances, it may result in harmful chemical reactions that destroy the soil around the area. The consequences of destroyed soil include poor plant development and bad soil quality.

Options for remediation of contaminated groundwater can be grouped into the following categories:
containing the pollutants to prevent them from migrating further
removing the pollutants from the aquifer
remediating the aquifer by either immobilizing or detoxifying the contaminants while they are still in the aquifer (in-situ)
treating the groundwater at its point of use
abandoning the use of this aquifer's groundwater and finding an alternative source of water

Writer-
Md. Sahedul Islam
Department Of ESDM
Noakhali Science & Technology University