Total Hg and methyl Hg distribution in sediments of selected Louisiana water bodies.

Sediment samples (543) collected from selected Louisiana streams and lakes were analyzed for total Hg and methyl Hg content. The average total Hg content among 543 samples was 92.3 +/- 95.1 microg kg(-1). The average methyl Hg content in the samples was 0.68 +/- 0.80 microg kg(-1). Methyl Hg accounted for an average of 0.73% of the total Hg in sediment. Linear regression analysis of total Hg versus methyl Hg content of the sediment showed methyl Hg content was significantly correlated to total Hg content of sediment (P > 0.01, n = 537) and sediment organic matter content. (P > 0.01, n = 536) Methyl Hg was also positively correlated to clay (P > 0.01, n = 537) and inversely correlated to sand content of sediment (P > 0.01, n = 537). Total Hg and methyl Hg content in these sediments was within the normal range reported elsewhere indicating no significant industrial or municipal Hg contamination. A comparison of selected water bodies with fishing advisories showed no relationship to total Hg and methyl Hg in sediment.

Total and methyl mercury in wetland soils and sediments of Louisiana's Pontchartrain Basin (USA).

Accumulation of methylmercury (MeHg) in aquatic biota is a primary toxicological concern associated with Hg contamination in the environment. This study reports total mercury (THg) and MeHg measurements in 11 swamp and 24 marsh soils/sediments in wetlands surrounding Lake Pontchartrain and Lake Maurepas located in Louisiana's Pontchartrain Basin. The salinity level ranged from fresh, brackish to salt water. Average THg content in the swamp soils/sediments (112.3 microg kg(-1), n = 10) was significantly higher (P = 0.04) than in the marsh soils/sediments (56.5 microg kg(-1), n = 24). The THg content in the marsh soils/sediments tended to decrease with salinity increase, probably due to geographical locations of the sampling sites with less Hg input in more saline regions. Average MeHg content in the soils/sediments was 1.3 microg kg(-1) (n = 34), higher than reported values in the bottom sediments of Lake Maurepas (0.8 microg kg(-1), n = 27) and Lake Pontchartrain (0.6 microg kg(-1), n = 147). Average MeHg/THg ratio in the marsh soils/sediments (0.022) was considerably higher than in the swamp soils/sediments (0.012). Analysis of MeHg/THg ratio along the salinity gradient at the marsh soils/sediments show that the highest MeHg/THg ratio (up to 0.040, n = 5) was found at the fresh/brackish water sites, and the lowest (0.002, n = 1) at the salt water site. Results suggest that there was a greater potential for MeHg formation in wetland soils/sediments than in bottom sediments of adjacent lakes. Results suggest that wetland surrounding the lakes may be a potential source of MeHg to the aquatic food chain and significance is governed by area of the adjacent wetland.

Immobilization of aqueous Hg(II) by mackinawite (FeS).

As one of the major constituents of acid volatile sulfide (AVS) in anoxic sediments, mackinawite (FeS) is known for its ability to scavenge trace metals. The interaction between aqueous Hg(II) (added as HgCl(2)) and synthetic FeS was studied via batch sorption experiments conducted under anaerobic conditions. Due to the release of H(+) during formation of hydrolyzed Hg(II) species which is more reactive than Hg(2+) in surface adsorption, the equilibrium pH decreased with the increase in Hg(II)/FeS molar ratio. Counteracting the loss of FeS solids at lower pH, the maximum capacity for FeS to remove aqueous Hg(II) was approximately 0.75 mol Hg(II) (mol FeS)(-1). The comparison of X-ray power diffraction (XRPD) patterns of synthetic FeS sorbent before and after sorption showed that the major products formed from the interaction between FeS and the aqueous Hg(II) were metacinnabar, cinnabar, and mercury iron sulfides. With the addition of FeS at 0.4 g L(-1) to a 1 mM Hg(II) solution with an initial pH of 5.6, Fe(2+) release was approximately 0.77 mol Fe(2+) per mol Hg(II) removed, suggesting that 77% of Hg(II) was removed via precipitation reaction under these conditions, with 23% of Hg(II) removed by adsorption. Aeration does not cause significant release of Hg(II) into the water phase.

Characterization of mercury and other heavy metals in sediment of an ecological important backwater area of River Tisza (Hungary).

Sediment from a representative and ecologically important backwater wetland under the influence of River Tisza (Hungary) was chemically characterized for sediment pollutants. Phosphine production potential, methyl mercury, mercury, and other heavy metals were determined along with other sediment chemical and physical properties. The wetland site, which is relatively isolated, represents an important bird reserve and nature conservation area. Methyl mercury and total mercury content was also low reflecting little mercury pollution in the sediment. Results of heavy metal analysis showed that only copper was elevated with concentration slightly above the reported levels considered excessive in soils and sediments. Other sediment properties were in normal range except boron content, which was high. Results show sediment were relatively unpolluted but should be routinely monitored to insure that this ecologically important area remains environmentally safe for future generation.

Total mercury and methylmercury in freshwater and salt marsh soils of the Mississippi river deltaic plain.

Mercury entering wetland environments can be microbially methylated to methylmercury. The purpose of this study was to investigate the historical rate of mercury accumulation and distribution of total and methylmercury in soil profile of Louisiana coastal marshes. Two sediment cores each were taken from Louisiana freshwater marsh and salt marsh. Vertical accretion was determined using the 137Cs dating technique. Total and methylmercury were determined with depth in the soil profiles. The fresh marsh soil on a dry weight basis contained more total and methylmercury than the salt marsh. Average vertical accretion rates in freshwater marsh and salt marsh were 0.90 and 0.75 cm year(-1), respectively. Average total and methylmercury content (to a depth of 30 cm) was 140 and 4.19 microg kg(-1) and 80 and 1.34 microg kg(-1) for the fresh and salt marsh, respectively. Due to greater sediment input resulting in a higher bulk density the salt marsh contained more total mercury per m2 (to 30 cm depth) than the fresh water marsh (5340 microg m(-2) as compared to 2929 microg m(-2)). The amount of methylmercury per m2 to depth of 30 cm was approximately the same for each marsh.