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Natural contaminant threat to drinking water from groundwater

 

16 March 2020

More than ​half of the ​world's ​population ​faces a looming ​threat to the ​quality and ​availability of ​their drinking ​water because ​climate change ​and urbanisation ​are expected to ​cause an ​increase in ​groundwater ​organic carbon, ​a new UNSW ​study has found.​

The research, ​published ​in  ​ Nature Communications  ​overnight, ​examined the ​largest global ​dataset of 9404 ​published and ​unpublished ​groundwater ​dissolved ​organic carbon (​DOC) concentrations ​from aquifers ​in 32 countries ​across six ​continents. ​

DOC is a ​naturally ​occurring ​component of ​groundwater, ​but the higher ​its concentration,​ the more ​difficult and ​expensive it is ​to make ​groundwater ​drinkable. In ​Australia, ​groundwater is ​widely used as ​the main source ​of drinking ​water for many ​cities and ​towns. ​

Lead author ​Dr Liza ​McDonough, of ​the Connected ​Waters ​Initiative ​Research Centre ​at UNSW, said ​the study ​forecasted ​elevated DOC ​concentrations ​because of ​projected ​changes in ​temperature and ​rainfall due to ​climate change, ​as well as ​increased ​urbanisation. ​

"We ​identified ​groundwater DOC ​concentration ​increases of up ​to 45 per cent, ​largely because ​of increased ​temperatures in ​the wettest ​quarter of the ​year -- for ​example, in a ​number of south-​eastern states ​in the United ​States. We ​predict ​increases in ​DOC in these ​locations could ​increase water ​costs for a ​family of four ​by US$134 per ​year," Dr ​McDonough said. ​

"Other areas ​such as eastern ​China, India ​and parts of ​Africa already ​experience ​severe ​groundwater ​contamination ​issues. These ​may be further ​compounded, ​particularly in ​south-eastern ​China, by ​groundwater DOC ​increases ​associated with ​large predicted ​increases in ​temperature in ​the wettest ​quarter of the ​year by 2050. ​

"Generally, ​we expect ​urbanisation to ​increase ​groundwater DOC ​concentrations ​by up to 19 per ​cent, compared ​to agricultural ​or natural land ​use, likely as ​the result of ​contamination --​ for example, ​through leaking ​septic and ​sewer systems." ​

The research, ​a collaboration ​between UNSW, ​the Australian ​Nuclear Science ​and Technology ​Organisation (​ANSTO), ​Southern Cross ​University, ​British ​Geological ​Survey, and the ​University of ​Bradford, found ​four major ​contributing ​factors to ​groundwater DOC ​levels: climate,​ land use, ​inorganic ​chemistry and ​aquifer age. ​

Health threat

Dr McDonough ​said increased ​groundwater DOC,​ whether ​naturally ​occurring or ​due to ​contamination, ​also posed a ​threat to human ​health. ​

"Groundwater ​is Earth's ​largest source ​of freshwater ​and provides ​essential ​drinking water ​for more than ​50 per cent of ​the world's ​population," ​she said. ​

"But, because ​most health ​impacts caused ​by DOC are ​related to the ​formation of by-​products of ​water treatment ​chlorination ​and depend on ​concentrations ​of other water ​chemical ​parameters, the ​World Health ​Organization ​and many ​countries -- ​including ​Australia -- do ​not regulate ​DOC concentrations ​in drinking ​water directly."​

Dr McDonough ​said that while ​DOC is a ​naturally ​occurring, key ​element of ​groundwater it ​could combine ​with, and ​transport, ​potentially ​dangerous heavy ​metals ​otherwise bound ​to rocks and ​sediment where ​groundwater ​occurs. ​

"This is a ​concern when, ​for example, ​more than 100,​000 lifetime ​cancer cases in ​the United ​States alone ​can be ​attributed to ​drinking water ​contaminants," ​she said. ​

Water ​treatment costs ​to rise ​

Dr McDonough ​said it was ​important to ​understand what ​caused high DOC ​concentrations ​in groundwater. ​

"An increase ​in groundwater ​DOC concentration ​impacts the ​ability and ​therefore cost ​to make ​groundwater ​drinkable," she ​said. ​

"For example, ​we projected a ​16 per cent ​increase in ​annual ​household water ​costs in some ​parts of the ​United States ​because of ​rising water ​treatment costs ​-- due to the ​need to ​implement ​additional ​water treatment ​measures to ​remove ​increased DOC ​concentrations. ​

"The decrease ​in groundwater ​quality and ​substantial ​increase in ​water treatment ​costs will also ​compound ​existing ​constraints on ​groundwater ​resources, ​including ​availability." ​

Wet vs arid climates

Dr McDonough ​said the ​impacts on ​groundwater DOC ​levels from ​climate change ​and urbanisation,​ while likely ​to occur ​globally, ​differed by ​geography and ​climate. ​

"Our research ​found that in ​arid climates, ​groundwater DOC ​concentrations ​increased with ​higher rainfall ​because ​microbes can ​better break ​down organic ​matter, such as ​leaves, under ​warm and ​increasingly ​wet conditions,"​ she said. ​

"Increased ​temperatures in ​arid environments,​ however, ​reduced ​groundwater DOC ​concentrations ​because when ​conditions are ​too hot and dry,​ vegetation and ​organic matter ​sources are ​limited. ​

"By contrast, ​increased rain ​in warm and wet ​environments ​decreased ​groundwater DOC ​concentrations ​because heavy ​rainfall ​dilutes the DOC ​in groundwater."​

Water treatment solutions

Dr McDonough ​said she looked ​forward to ​conducting ​further ​research to ​determine the ​best water ​treatment ​options for ​areas where ​groundwater DOC ​concentrations ​are anticipated ​to increase. ​

"Our next ​step is to ​investigate how ​the character ​of DOC changes ​when you have ​different ​aquifer ​minerals, ​because some ​types of ​organic matter ​can stick to ​certain mineral ​surfaces and ​ultimately ​reduce this ​type of organic ​matter ​remaining in ​the water," she ​said. ​

"This will ​help provide ​guidance on the ​most suitable ​water treatment ​options in ​areas where DOC ​concentrations ​are expected to ​increase." ​

FULL PAPER AND ​SOURCE SCIENCE ​DAILY ​University of ​South ​Wales

Source :https://thewaternetwork.com/article-FfV/natural-contaminant-threat-to-drinking-water-from-groundwater-tnHZJGV5Nss04hj7zOWS0Q

 

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