Behavior of potential toxic elements (PTEs) in the Aquatic Environment

Rivers are the lifelines of civilisations. Mankind has built cities that have prospered and progressed on the banks of rivers from ancient times. Rivers are vital for us – as a source of water, for navigation and in a lot of other ways – and therefore we have to protect them from pollution.

The contamination of river basins is mainly due to the accumulation of heavy metals and semi-metals (termed metalloids) from different human activities and natural sources. Potentially toxic elements (PTEs) such as Cadmium (Cd), Copper (Cu), Chromium (Cr), Lead (Pb), Nickel (Ni), Arsenic (As) and Zinc (Zn) are the most critical long-term hazards in the aquatic environment. PTEs tend to bioaccumulate in animals and plants and adversely affect local communities as well as aquatic flora and fauna.

Surface water is more vulnerable because contaminants are disposed of there. Once they enter the human body, the majority of toxic elements are adsorbed, accumulated, and bio-magnified causing a wide variety of diseases.

The behaviour of PTEs in the water bodies is largely controlled by the regional geology, geochemical activity (dissolution and precipitation), climatic conditions, and Physico-chemical parameters. Additionally, surface or groundwater quality is also influenced by various geochemical processes that occur under human

interference. The chemistry of water bodies is controlled by bio-chemical reactions and geo-chemical processes like dissolution, hydrolysis, precipitation, adsorption, ion exchange, and oxidation-reduction

The study on microbially-mediated metals and nitrogen interactions in sediments and water bodies has received great attention in the last few years. Metal-reducing bacteria have the potential to alter the water and sediment geo-chemistry. This directly or indirectly affects the speciation and mobility of contaminant metals within natural environments. Several bacteria and mycorrhizal fungi, symbiotically attached to a plant, play an important role in the solubilisation of various microbially-mediated metals.

In the aquatic system, microorganisms are involved in various biogeochemical processes such as assimilation or adsorption and mineralization; dissolution and precipitation; oxidation and reduction; and methylation and de-alkylation.  The biogeochemical cycling of nitrogen – which has multiple oxidation states – form various complexes with Iron, Manganese, Uranium, and Chromium. Additionally, microbial transformations occur with some metalloid elements, such as Arsenic, Selenium, and Tellurium.

These pieces of evidence indicate that such contaminants directly or indirectly influence the biogeochemical cycle. Therefore, it is important to understand the biogeochemical processes in sediments and water which would help us to evaluate the parent source of contaminants.

Proper steps to be taken to gain knowledge about this phenomenon

To tackle the increasing contamination of the aquatic environment professional and experienced organisations take these following steps:

  • Reviewing how the microbial mechanisms contribute to the cycling of PTEs in sediment and
    groundwater and choose suitable analytical techniques for testing under prevailing geographical conditions.
  • Evaluate the geochemical properties and enrichment of PTEs in sediment and water.
  • Identify the compositional groups, critical parameters, and biogeochemical processes that are prevalent in the study area.
  • Investigate the co-occurrence of nitrogen and their various complexes with metals as well as the correlation of additional geochemical parameters in sediment and groundwater to evaluate the fate and transport of contaminants.
  • Examine the spatial variation of microbially-mediated metals and nitrogen in sediment and groundwater to find out their trends and possible sources.
  • Study the degrees of microbial mediation of metals and nitrogen using some standard microbial strains isolated previously from a similar type of sediment.
  • Determining the potential risk of PTEs and geochemical parameters for regional populations and aquatic systems.
  • Collecting the necessary secondary data to identify regional geology, population, climatic condition for populating the chosen techniques, and map-making.

A Technical Study will be based on the following procedure:

  1. Initially, different water and sediment samples will be taken from the river basin based on the sampling method suggested by the American Public Health Association (APHA, 2005) and the United States Environmental Protection Agency (USEPA, 1992). A preliminary reconnaissance survey of the entire study area will be done before the sampling to locate the sampling point. During a reconnaissance survey, all necessary investigation shall be carried out including existing drainage patterns, land elevation, sediment texture, land use pattern, and physiographical condition.
  2. The physical parameters like acidity, electrical conductivity, total dissolved solids, oxidation-reduction potential, and dissolved oxygen (pH, EC, TDS, ORP, and DO) will be measured at the sampling site itself since these are very sensitive to change. The vertical distribution of nitrogen and geochemical parameters in the sediment will be measured to appraise the composition and leaching effects and mobility.
  3. The efficacy of the micro-organism to mobilization will be a consideration. The PTEs will be studied in the laboratory to evaluate the toxicity of metals to indigenous benthic organisms based.

Clean waters are not only a part of a healthy overall ecosystem but also directly responsible for the health of flora and fauna and human life in the locality. With the proper and professional study of samples, we know how to take care of the aquatic environment – which is essential for healthy living all around. In today’s world, such expertise and knowledge are not just desirable but vital for life to exist and thrive.

Writer Name: Dipak Nayak