Inorganic arsenic and manganese are the most widespread elemental contaminants of potable water around the world. Being mainly of natural (geogenic) origin, arsenic and manganese are released from sediments in the subsurface as a result of unfavorable geochemical conditions and can occur in groundwater at concentrations of more than 1000 micrograms per liter of water. The safety limits for arsenic in drinking water in most countries are 10 or 50 and, for manganese 400 micrograms per liter (µg/liter).
Arsenic leads to chronic poisoning if ingested regularly in small doses and is an acute problem in Vietnam and many regions of Southern Asia (i.e., Bangladesh, Cambodia, India, Myanmar, Nepal, Pakistan, Sumatra (Indonesia). It is also found in drinking waters of other countries, such as Argentina, China, Croatia, Hungary, Mexico, New Zealand, Romania and the United States. Manifestations of chronic arsenic poisoning are severe health problems, such as skin lesions, hyperkeratosis, melanosis, skin cancer and cancer of internal organs. Manganese is particularly harmful for newborns and children as it hampers the intellectual development of the child.
The Red River delta in Vietnam is one of the most densely populated regions in the world. In 1998 the arsenic problem in Vietnam was identified in the capital city of Hanoi and surrounding rural districts and has since been recognized in other locations of the Red River delta [see Berg et al. 2001 and Winkel et al. 2011]. To identify safe and unsafe areas over the entire Red River delta, a large-scale hydrogeochemical groundwater survey was launched in 2005. It included the analysis of arsenic, manganese, selenium, boron, iron, salinity, phosphate, ammonium, sulfate, dissolved organic carbon, and 30 further chemical parameters. Concentration maps and arsenic risk modeling suggest that several million inhabitants of the Red River delta are at risk of chronic arsenic and/or manganese poisoning.
The data of the extensive groundwater survey in the Red River (Vietnam) is presented as a hydrochemical atlas comprising 42 different chemical parameters. We found that 65% of all studied wells exceed the WHO guideline values for arsenic, manganese, barium, selenium or a combination of these elements. Correspondingly, geogenic groundwater pollution in the Red River delta poses a serious long-term health threat to about 7 million people. This is particularly worrying since groundwater is the main source of drinking water.