Environmental Issues

Mercury in natural waters occurs in different forms including elemental mercury (Hg0), ionic mercury (Hg, Hg2), and methylated mercury CH3Hg, (CH3)2Hg (Ravichandran, 2003). On the other hand, industrial processes especially those which involve production of electricity help introduce Mercury as an atmospheric emission spreading across the plant and settles back to the surface becoming aquatic contaminants in rivers, lakes and oceans.

Nitrate leaching has proven to affect farming especially cropping systems as well as fishing areas by building up in agricultural environments and contaminating natural waters.  Studies found that the degree of Nitrate in organic farming systems vary from conventional systems. Organic farming bears lower N input. However, no evidence proves that nitrate leaching will be reduced by organic farming. Counter- measures have been pursued by later researches geared towards environmental concerns particularly sustainable farming systems.

In a study of in-stream bioreactor using coarse wood-particle media to treat agricultural drainage of nitrate in southern Ontario, a gravel riffle in the streambed was constructed. This method can be used to facilitate nitrate removal in the reactor in huge volumes. Reduction of nitrate in woodchips sustains hydraulic conductivity or high permeability.

Monomethyl mercury (CH3Hg) in aquatic ecosystems accumulates under sulfate-reducing conditions. An examination of  patterns involving CH3Hgconcentrations in the hypolimnion of a dimictic lake, increases in NO3 inputs. Decreased CH3Hg in the anoxichypolimnion results in a reduced deposit of organic matter while increasing in NO3 concentrations.when NO3- was abundant, CH3Hg concentrations lowered. The effect of NO3  to CH3Hg  accumulation thrives in oxygen-limited freshwater and terrestrial environments. It is believed to have a significant relation to the biogeochemistry of mercury.

The bioaccumulation of mercury and Methylmercury in aqueous environments has been linked by studies to the presence of dissolved organic matters (DOM). DOM binds trace metals effectively affecting their speciation, solubility, mobility and toxicity. In studies conducted throughout the years, strong evidence points to the conclusion that DOM interact very strongly with mercury by helping it form an extremely strong ionic bond with reduced sulfur sites. Reduced SO4 promotes formation of MeHg which helps in treating nitrate in agricultural environments.

A potentially important vector for Hg transport from the epilimnion into the hypolimnion is the settling particulate organic matter. Its microbial respiration produces anoxic conditions which promote reduction of sediment Fe and Mn hydrous oxides releasing the reduced form  into the overlying water. The  large adsorption capacities of Fe and Mn can control the concentrations of other ions and dissolved organic matter significantly controlling Hg and MeHg distributions.

Mercury (Hg) being bioaccumulative and a highly toxic contaminant especially in the MeHg form is presently concentrated in aquatic environments at levels considered a health risk to humans and wildlife. Nevertheless, the formation of MeHg in reduced sulfur sites does good to treatment of nitrate.