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Mercury Toxicity
Published in Edgardo R. Donati, Heavy Metals in the Environment, 2018
Mohammed H. Abu-Dieyeh, Kamal Usman, Haya Alduroobi, Mohammad Al-Ghouti
Methylation and bioaccumulation constitutes important components in the mercury geo-chemical cycle found in different aquatic environmental phases, water, the sediment, and biota. In fishes, for instance, mercury is majorly found in methyl mercury (CH3Hg) form and conversion from ionic to mono methyl mercury form is critical to fish bioaccumulation, exposure, and toxicity to living organisms including humans (Randall and Chattopadhyay, 2013). Complexation with dissolved organic matter in bacterial mediated methylation is expressed and measured as dissolved organic carbon and is crucial to the bioavailability of mercury. The more the dissolved organic matter, the less is the availability of inorganic mercury thereby limiting organismic uptake. In sulfur limited environment, the dissolved organic matter stimulate microbial growth and hence improve the rate of mercury methylation in sediments and aqueous phases (Graham et al., 2012; Kelly et al., 2003).
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Published in Alina Kabata-Pendias, Barbara Szteke, Trace Elements in Abiotic and Biotic Environments, 2015
Alina Kabata-Pendias, Barbara Szteke
Mercury methylation and bioaccumulation in water depend on several parameters, such as Hg loading, microbial activity, pH and redox potential, temperature, and several other factors. Me–Hg species are relatively easily accumulated by water biota (Perelomov and Chulin 2013). A great part (>95%) of total Hg in both, fresh and saltwater fish is in the form of Me–Hg. It is taken up by fish straight from the water, as well as from their fodder. In general, the highest Hg content is in fish muscles and the lowest is in gonads. In muscles of fish from the Baltic Sea, its contents vary between 0.2 and 0.33 mg/kg, whereas in female gonads its range is 0.02–0.05 mg/kg (Voigt videKabata-Pendias and Mukherjee 2007). The highest means Hg levels in commercial fish in the United States are reported to be 0.73 and 1.45 mg/kg FW, in mackerel king and tilefish, respectively; and the lowest contents are 0.01 and 0.11 mg/kg FW, in salmon and cod, respectively.
Seasonal patterns of methylmercury production, release, and degradation in profundal sediment of a hypereutrophic reservoir
Published in Lake and Reservoir Management, 2021
Byran Fuhrmann, Marc Beutel, Priya Ganguli, Liying Zhao, Sarah Brower, Andrew Funk, Jeffrey Pasek
In the process of mercury methylation, iHg is transformed into organic methylmercury (MeHg) by anaerobic bacteria (Bigham et al. 2017). The anaerobic bacteria specifically implicated in the production of MeHg include sulfate-reducing bacteria (SRB), iron(III)-reducing bacteria (IRB), methanogens, and a small number of fermenters (Podar et al. 2015). Although not all anaerobic bacteria are capable of mercury methylation, no known aerobic bacteria have been identified, and MeHg typically accumulates in bottom waters under anaerobic conditions (Podar et al. 2015). MeHg can be converted back into either iHg or Hg0 by a process known as demethylation. MeHg demethylation can occur due to abiotic or biotic processes (Bigham et al. 2017). Abiotic demethylation primarily occurs in the surface water of lakes and reservoirs when MeHg is exposed to ultraviolet (UV) light (Paranjape and Hall 2017). Biotic demethylation has been demonstrated by a variety of microorganisms and multiple pathways have been identified (Ullrich et al. 2001). Although aerobic organisms have generally been found to express a greater ability to demethylate MeHg, there is a growing body of evidence that anaerobic organisms such as SRB and methanogens are prominent demethylators in freshwater sediments (Korthals and Winfrey 1987, Pak and Bartha 1998, Ullrich et al. 2001, Kronberg et al. 2018, Beutel et al. 2020). It is important to consider that both iHg methylation and MeHg demethylation play important roles in regulating the net pool of MeHg in aquatic environments.
Health risk assessment of lead, mercury, and other metal(loid)s: A potential threat to the population consuming fish inhabiting, a lentic ecosystem in Steel City (Jamshedpur), India
Published in Human and Ecological Risk Assessment: An International Journal, 2019
Preeti Kumari, Subodh Kumar Maiti
There are variations in the concentration of metal(loid)s in fish organs. Based on the maximum metal(loid)s concentrations, it is observed that gill, liver, and intestine are the major metal(loid) accumulating organs. The maximum concentration of As and Cr is found in gill might be due to the reason that this organ is the most exposed part of fish which facilitates it to accumulate more metal(loid)s in comparison to other organs. Higher concentration of As and Cr in gill represents the elevated concentration of these metal(loid)s in surrounding water (Pandey et al.2017). The maximum concentration of Cd and Pb is reported in the liver of the six selected fish species. This indicates a long-term pre-deposited Cd and Pb exposure from the aquatic environment (Pandey et al. 2017). Several authors have reported the higher concentration of metal(loid)s in the liver in comparison to other tissue/organs (Turkmen et al.2009; Vinodhini and Narayanan 2008). A comparatively higher Cu and Hg concentration in the intestine of fish indicate that these metals may enter as a component of sediment fraction and their sources are probably contaminated water and food (Copaja et al.2017; Jayaprakash et al.2015). Higher Hg concentration in the intestine may be due to the process of mercury methylation carried out in the intestine. Mercury methylation is the biochemical process of conversion of ingested mercury into methylmercury by certain bacteria present in the fish intestine (Ali and Khan 2018). The lower metal(loid) concentration in muscle suggests the low-fat affinity to bind with this element probably due to the high presence of calcium in muscle (Ali and Khan 2018; Jayaprakash et al.2015).