The　demethylation　potential　of　pollutants　is　arguably　an　innate　component　of　their　toxicity　in　environmental　samples.　A　method　was　developed　for　determining　the　total　demethylation　potential　of　food　samples　(TDQ).　The　demethylation　epigenetic　toxicity　was　determined　using　the　Hep　G2　cell　line　transfected　with　pEGFP-C3　plasmids　containing　a　methylated　promoter　of　the　EGFP　reporter　gene.　The　total　demethylation　potential　of　the　sample　extracts　(the　5-AZA-CdR　demethylation　toxic　equivalency)　can　be　quantified　within　one　week　by　using　a　standard　curve　of　the　5-AZA-CdR　demethylation　agent.　To　explore.　the　applicability　of　TDQ　for　environmental　samples,　17　groundwater　samples　were　collected　from　heavy　polluted　Kuihe　river　and　the　total　demethylation　potentials　of　the　sample　extracts　were　measured　successfully.　Meaningful　demethylation　toxic　equivalencies　ranging　from　0.00050　to　0.01747　mu　M　were　found　in　all　groundwater　sample　extracts.　Among　19　kinds　of　inorganic　substance,　As　and　Cd　played　important　roles　for　individual　contribution　to　the　total　demethylation　epigenetic　toxicity.　The　TDQassay　is　reliable　and　fast　for　quantifying　the　DNA　demethylation　potential　of　environmental　sample　extracts,　which　may　improve　epigenetic　toxicity　evaluations　for　human　risk　assessment,　and　the　consistent　consuming　of　groundwater　alongside　the　Kuihe　river　pose　unexpected　epigenetic　health　risk　to　the　local　residents.　(C)　2015　Elsevier　B.V.　All　rights　reserved.