For 10 years, the town of Denmark injected a chemical into its drinking water that has rarely, if ever, been used in public water systems across the country. The chemical was supposed to kill bacteria that threatened one of the towns wells. But after questions surfaced last spring, state regulators ordered the town to stop putting the chemical into its aging water system, according to records reviewed by The State newspaper. Now, state and federal environmental agencies are trying to determine whether the chemical, called HaloSan, is suitable for use in a public water system. The material, more commonly used to disinfect hot tubs, could have toxic effects on people if not administered in the proper doses. Questions about HaloSan were highlighted in a CNN report recently on drinking water complaints in Denmark. The news network said the material was not approved by the EPA for use in drinking water. CNN first reported on the use of HaloSan by Denmark officials. Marc Edwards, a Virginia Tech researcher who helped unravel the Flint, Mich., water crisis, said Denmark made a mistake in using HaloSan. Edwards and researchers at the University of South Carolina ran across the HaloSan issue while examining drinking water issues in Denmark earlier this year. That chemical never should have been added to a public water supply, he said. When I saw this, I was shocked. Denmark, a town of about 3,000 people in Bamberg County, had used the material since 2008 after the S.C. Department of Health and Environmental Control gave its authorisation. But in a July decision ordering Denmark to stop using HaloSan, regulators at Clemson University said the product was not registered by the U.S. Environmental Protection Agency, records show. Denmark Mayor Gerald Wright said he relied on DHEC to provide us with the advice on what we needed to do to have our system as it should be. Efforts to reach a company that markets HaloSan were unsuccessful. Some residents of Denmark have complained for years about the quality of the towns drinking water, saying it often comes out of the tap muddy or discoloured. Questions also have surfaced about whether lead is washing from pipes into peoples tap water. The town has been the subject of multiple DHEC enforcement actions in the past 15 years. But Wright said the town has made improvements, and many of the complaints about the water system are coming from a handful of political rivals in Denmark. It has been an annoying situation for me because I know much of what has been done and said is a lot to do about nothing, Wright said. HaloSan has not been used by other drinking water systems across the country, according to Edwards and emails involving EPA officials. Most rely on chlorine products to kill bacteria. Have never heard of its usage before, according to one EPA official quoted in an email obtained by The State. Edwards questioned DHEC last May about the material. Has feeding of this chemical previously been disclosed to Denmark residents? Edwards asked DHEC officials in a May 24 email. I was never told or read anything about this before. Edwards has been conducting research on the Denmark water after residents complained about discoloured water. Much of his research has focused on water coming from peoples taps. Wright denied Edwards request earlier this year to test Denmarks water supply wells. But Wright did let DHEC, the University of South Carolina and the Edisto Riverkeeper test the water. Like DHEC and the Riverkeeper, USC did not find contamination in the towns water supply wells. Edwards said it may never be known whether the proper doses of HaloSan were used in Denmarks water supply because records are lacking. Carolina researcher Susan Richardson, a former EPA official who now teaches at the university, said shes been told that HaloSan was approved and safe for use. The information we got from DHEC, and they involved … EPA in this, too, showed that when it is used for drinking water, it is supposed to be safe, she said. The toxicity data I saw did not give me any concern.