Abatement of Chromium (VI) and Mobilization of Selected Pollutants Including Cr(VI) in Aquatic Food Chain

Abstract

In the backdrop of increasing freshwater demand, the wastewater treatment and recycling seems to be the option at least for purposes other than drinking. Among various types of pollutions in aquatic systems, heavy metal contamination is of major concern because of their potential threat to both humanity and aquatic organisms. Because of high toxicity, arsenic, cadmium, chromium, lead and mercury rank among the priority metals, some of which like chromium (VI) are even documented as carcinogen. However, some of these metals are needed as micronutrient; nonetheless, their increased concentration can be dangerous or even be hazardous. Chromium (VI) is 500 times more toxic than Cr (III) state and its human toxicity is unveiled by skin irritation, lung cancer, as well as kidney, liver and gastric damage. Present dissertation is focused on Chromium (VI) related pollution, it’s abatement and threat of impending bioaccumulation of Chromium (VI) and persistent organic pollutants (POPs’) in various trophic levels.
Modern method of biosorption often utilizes dead biomass, which does not require nutrients and may be exposed to situations of high toxicity. In the present dissertation, the marine water green algae was economically as well as effectively used as a biosorbent and the physical adsorption was observed. The effect of various parameters like pH, temperature, initial dose of the adsorbent, initial contaminant concentration was experimented. The reusability as well as the effect of presence of other cations and anions were also examined. Dead algal biomass exhibited 89 % Chromium (VI) removal.
The live algal cells of Chlorella sp. were used for removal of Chromium (VI) with 93 % efficiency. The experiments were conducted using OVAT approach. NTA, being an agent used in 𝐶𝑂2 absorption, hence the resultant bi-carbonate solution was used as a carbon source for the growth of algae. This small incident can open up a huge possibility of using live algal cell for dual purposes: for heavy metal removal from contaminated aquatic sources with consequential and simultaneous 𝐶𝑂2 sequestration. The effect parameters including initial metal ion concentration, initial biomass concentration, and pH were studied on the metal removal ability of Chlorella sp. As far as Chromium (VI) removal by live algal biomass is concerned, the remediation can be attributed to bio adsorption and bioaccumulation.
Experiments were conducted in particular algae (chlorella sp.), a fish (gourami) and a two organism food chain in a simulated water body contaminated with chromium (VI) to study the different bioaccumulation metrics including bioconcentration factor, bioaccumulation factor, biomagnification factor, and trophic magnification factor.
In the present research endeavor, Chromium (VI) was transferred to dead algal biomass, which acted as a sink and remained in the environment. To remove Chromium (VI) much efficiently, live algal biomass was used as a sink and instituted in the environment. Both the sinks later would offer themselves as potential source of bioaccumulation. Hence, it was a conscious decision to investigate the mobility of Chromium (VI); consequently, bioaccumulation in aquatic food chain.
Ten numbers of persistent organic pollutants and a four membered aquatic food chain was considered to conduct a simulated investigation on bioaccumulation among organisms in different trophic levels. The biomagnification of them in all trophic levels remained more than 1.0, with alarmingly high values for some of the chemicals (about 3.14 for PCB; 2.5 for DDT and 2.15 for chlordane) showing their resistance to biodegradation with progression of trophic levels. The policy makers/administration should be in close contact to the scientific community and monitoring agencies to control /band the production of any suspected toxic and persistent organic chemicals.
In an ending note:
Since we have no sink dedicated to throw those pollutants; except mother earth, we need to axe our desire for products leading to an impending annihilation of aquatic life and humankind.