Mercury in Fish from a Sulfate-Amended Wetland Mesocosm

1 This study used an experimental model of a constructed wetland to evaluate the risk of 2 mercury methylation when the soil is amended with sulfate. The model was planted with 3 Schoenoplectus californicus, and the sediments were varied during construction to 4 provide a control and two levels of sulfate treatment. This allowed characterization of 5 sulfate’s effect on mercury bioaccumulation in periphyton and two species of fish – 6 eastern mosquitofish (Gambusia holbrooki) and lake chubsucker (Erimyzon sucetta). 7 After one year in the experimental model, mean dry-weight normalized total mercury 8 concentrations in mosquitofish from the non-sulfate treated controls (374 ± 77 ng/g) and 9 the reference location (233 ± 27 ng/g) were significantly lower than those from the low 10 and high sulfate treatments (520 ± 73 and 613 ± 80 ng/g, respectively). For lake 11 chubsucker, mean total mercury concentration in fish from the high sulfate treatment 12 (276 ± 63 ng/g) was significantly elevated over that observed in the control (109 ± 47 13 ng/g), the low sulfate treatment (122 ± 42 ng/g), and the reference population (41 ± 2 14 ng/g). Methylmercury in periphyton ranged from 6.6 ng/g (dry weight) in the control to 15 9.8 ng/g in the high sulfate treatment, while total mercury concentrations ranged from 16 1148 ng/g in the control to 1297 ng/g in the low sulfate treatment. Fish methylmercury 17 bioaccumulation factors from sediment ranged from 52 to 390 and from 495 to 3059 for 18 water. Based on these results, it can be concluded that sulfate treatments add a factor of 19 risk due to elevated production of methylmercury in sediment and porewater which 20 biomagnified into small fish, and may potentially increase through the food web. 21 22