Mercury sequestration and transformation in chemically enhanced treatment wetlands

Philip A M Bachand; Tamara E C Kraus; Elizabeth B Stumpner; Sandra M Bachand; Dylan Stern; Yan Ling Liang; William R Horwath

doi:10.1016/j.chemosphere.2018.10.144

Mercury sequestration and transformation in chemically enhanced treatment wetlands

Chemosphere. 2019 Feb:217:496-506. doi: 10.1016/j.chemosphere.2018.10.144. Epub 2018 Oct 27.

Authors

Philip A M Bachand¹, Tamara E C Kraus², Elizabeth B Stumpner³, Sandra M Bachand⁴, Dylan Stern⁵, Yan Ling Liang⁶, William R Horwath⁷

Affiliations

¹ Bachand & Associates, 231 G St., Ste. 28, Davis, CA 95616, USA. Electronic address: philip@bachandassociates.com.
² U.S. Geological Survey California Water Science Center, 6000 J Street Placer Hall, Sacramento, CA, 95819, USA. Electronic address: tkraus@usgs.gov.
³ U.S. Geological Survey California Water Science Center, 6000 J Street Placer Hall, Sacramento, CA, 95819, USA. Electronic address: estumpner@usgs.govd.
⁴ Bachand & Associates, 231 G St., Ste. 28, Davis, CA 95616, USA. Electronic address: sandra@bachandassociates.com.
⁵ Bachand & Associates, 231 G St., Ste. 28, Davis, CA 95616, USA; Delta Stewardship Council, 980 Ninth Street Ste 1500, Sacramento, CA 95814, USA. Electronic address: Dylan.Stern@deltacouncil.ca.gov.
⁶ Bachand & Associates, 231 G St., Ste. 28, Davis, CA 95616, USA; Department of Land, Air and Water Resources, 1 Shields Avenue, University of California Davis, Davis, CA, 95616, USA. Electronic address: yanliang@ucdavis.edu.
⁷ Department of Land, Air and Water Resources, 1 Shields Avenue, University of California Davis, Davis, CA, 95616, USA. Electronic address: wrhorwath@ucdavis.edu.

PMID: 30439661
DOI: 10.1016/j.chemosphere.2018.10.144

Abstract

Mercury (Hg) pollution is a concern to human and wildlife health worldwide, and management strategies that reduce Hg inputs to aquatic systems are of broad interest. Using a replicated field-scale study in California's Sacramento-San Joaquin Delta, we tested the effectiveness of chemically enhanced treatment wetlands (CETWs) under two coagulation treatments, polyaluminum chloride (Al treatment) and ferric sulfate (Fe treatment), in their initial removal and longer-term sequestration of Hg compared to untreated control wetlands. The primary mechanism for Hg removal by CETWs was the transfer of Hg from filtered forms to insoluble particulate forms and enhanced settling of particles. CETWs resulted in total Hg annual load removals of 63 ng m^-2 yr^-1 (71%) and 54 ng m^-2 yr^-1 (54%) for the Al and Fe treatments, respectively. Control wetlands removed significantly less at 13 ng m^-2 yr^-1 (14%). Load removals indicate that Fe treatment wetlands more effectively reduced filtered and total methylmercury (MeHg) exports, while Al treatment wetlands more effectively reduced particulate MeHg and total Hg exports. These differences in Hg species load reductions possibly indicate different mechanisms of Hg sequestration; current data suggest more effective floc formation and particle settling was likely responsible for the Al treatment behavior, while either preferential MeHg sequestration or methylation suppression was potentially responsible for Fe treatment behavior. Differences in Hg sequestration behavior post-coagulation between the flocs formed by different coagulants indicate the importance of in-situ studies and the need for careful selection of coagulant treatment depending on the Hg species requiring remediation.

Keywords: Agricultural drain water; Constructed wetlands; Mercury; Methylation; Sacramento-San Joaquin Delta; Water treatment.

MeSH terms

Environmental Monitoring / methods*
Environmental Pollution
Humans
Mercury / analysis
Mercury / chemistry*
Wetlands

Substances

Mercury