Bioaccumulation of methylmercury in a marine diatom and the influence of dissolved organic matter

Abstract

The largest bioconcentration step of most metals, including methylmercury (MeHg), in aquatic biota is from water to phytoplankton, but the extent to which dissolved organic matter (DOM) affects this process for MeHg largely remains unexplored in marine systems. This study investigated the influence of specific sulfur-containing organic compounds and naturally occurring DOM on the accumulation of MeHg in a marine diatom Thalassiosira pseudonana. Initial uptake rate constants and volume concentration factors (VCFs) of MeHg were calculated to evaluate MeHg enrichment in algal cells in the presence of a range of organic compound concentrations. At environmentally realistic and higher concentrations, the addition of glycine and methionine had no effect on algal MeHg uptake, but thiol-containing compounds such as cysteine and thioglycolic acid reduced MeHg accumulation in algal cells at high added concentrations (> 100 times higher than naturally occurring concentrations). However, environmentally realistic concentrations of glutathione, another thiol-containing compound as low as 10 nM, resulted in a decline of ~ 30% in VCFs, suggesting its possible importance in natural waters. Humic acid additions of 0.1 and 0.5 mg C/L also reduced MeHg VCFs by ~ 15% and ~ 25%, respectively. The bioaccumulation of MeHg for T. pseudonana in coastal waters with varying levels of dissolved organic carbon (DOC) was inversely correlated with bulk DOC concentrations. Generally, naturally occurring DOM, particularly certain thiol-containing compounds, can reduce MeHg uptake by phytoplankton.

Organic carbon content drives methylmercury levels in the water column and in estuarine food webs across latitudes in the Northeast United States

“…6b). This corresponds with higher densities of marine phytoplankton (as Chl-a) at high tides, which can bioconcentrate MeHg by about 10 5 times relative to seawater (Lee and Fisher, 2017;Schartup et al, 2018). The differences in Chl-a across regions, where phytoplankton productivity is higher in the southern sites, makes its relationship with MeHg concentrations difficult to isolate from other factors in estuarine systems.…”

“…Differences in BAF were most evident at sites associated with large coastal marsh areas (BH, BI, PC) and those having the largest differences in DOC concentration (BH and BI). While DOC increases the solubility and stability of MeHg in the water column in estuaries (Bergamaschi et al, 2011;Mitchell et al, 2012), it also decreases the bioavailability of MeHg at the base of the foodweb (Lee and Fisher, 2017;Luengen et al, 2012). Differences in DOC quality have been suggested to effect MeHg bioavailability, where humic fractions of terrestrial or wetland-derived DOC have been found to form DOC-MeHg complexes with low bioavailability (Schartup et al, 2015b).…”

“…While watershed inputs of terrestrial DOC have been associated with transport of MeHg to estuarine ecosystems (Conaway et al, 2003), complexation of MeHg to DOC decreases its availability for uptake at the base of the foodweb (Lee and Fisher, 2017;Luengen et al, 2012). In addition, increased inputs of terrestrial DOC may also flocculate during estuarine mixing, becoming a sink for MeHg (Soerensen et al, 2017), and higher DOC will decrease photodemethylation, which requires light penetration in the water column (DiMento and Mason, 2017).…”

Mercury in cetaceans: Exposure, bioaccumulation and toxicity

“…1). The methylation of mercury resulting from these abiotic and biotic processes is affected by a range of factors including pH, temperature, solar radiation, organic matter remineralisation, and the availability of sulphates and organic carbon (Lee and Fisher 2017). Overall, through a combination of these processes, methylmercury is the most common form of organic mercury in the marine environment and bio-magnifies most readily up the food chain (see below).…”

Utilización de microalgas como alternativa para la remoción de metales pesados

“…Las investigaciones científicas actuales han volcado la mirada a los bioadsorbentes como las microalgas, debido a su gran variedad, abundancia, disponibilidad de las diferentes especies, buena capacidad para absorber iones metálicos (Yin et al, 2019;Gutiérrez-Benítez et al, 2014), alta eficiencia, bajo costo y respeto con el ambiente (Yin et al, 2019;Vitola et al, 2018). Además, cuentan con diferentes mecanismos bioquímicos de captación de metales pesados (Lee & Fisher, 2017) y neutralización de la toxicidad (Yin et al, 2019;Bilal et al, 2018). No obstante, el crecimiento de las microalgas está limitado por factores como la carga contaminante, la presencia de nutrientes, la salinidad, el pH, la luz, CO2, etc.…”