Trace Metals in Otamiri River Biofilms: Owerri, Nigeria | InformativeBD

Dike Henry Ogbuagu, Chidiogo Grace Okoli, Enos Ihediohamma Emereibeole, Ikechukwu Chimezie Anyanwu, Osinachi Onuoha, Nkiruka Onyekachi Ubah, Chibueze Oscar Ndugbu, Obinna N. Okoroama, Arthur Okafor, Edu Ewa, Rex Ossai, and Favour Ukah, from the different institute of the  Nigeria. wrote a research article about, Trace Metals in Otamiri River Biofilms: Owerri, Nigeria. entitled, Trace metals accumulation in biofilms of the upper and middle reaches of Otamiri river in Owerri, Nigeria. This research paper published by the Journal of Biodiversity and Environmental Sciences (JBES). an open access scholarly research journal on Biodiversity. under the affiliation of the International Network For Natural Sciences | NNSpub. an open access multidisciplinary research journal publisher.

Abstract

This study utilized biofilms as model in ecotoxicology to estimate pollutant loading of a natural water body. Water samples were collected from six sampling locations sited between the upper and middle courses of the Otamiri River in the southeastern city of Owerri, Nigeria and fixed with conc. HNO3. Biofilms were grown in microcosms housing serially arranged sterile glass slides at the sampling locations, harvested after 1, 2 and 3 weeks, minced in sterile sample bottles with distilled water and fixed with conc. HNO3. Natural biofilms were also collected from submerged surfaces and fixed. Pb, Cu and Cd contents were determined in samples with atomic absorption spectrophotometer. The studentized t-test was used to compare trace metals levels in water column and biofilms, while single factor ANOVA was used to determine spatial homogeneity in mean variance. Mean Pb concentrations ranged from 1.5950-3.2900 (2.4303 ± 0.0835) mg/kg, Cu from 4.2934-7.5020 (5.6212 ± 0.1938) mg/kg and Cd from 0.0308-1.0559 (0.2082 ± 0.0005) mg/kg in the slide biofilms. However, they ranged from 0.0017-0.0267 (0.0150 ± 0.0003), 0.0333-0.6067 (0.2047 ± 0.0929) mg/L and totally undetected, respectively in water columns. Trace metals levels in slide and natural biofilms differed very markedly from those in water column (sig. t-values = 0.000, each), even as levels in slide and natural biofilms did not (sig. t-value = 0.747) at P<0.05. Pb and Cu concentrations increased from location 1 to 6 in both water columns and biofilms, even as there was homogeneity in spatial mean variances in slide [F(1.1458)<Fcrit(4.1300)] and natural biofilms concentrations [F(1.2812)<Fcrit(4.1300)] at P<0.05. Although mean Pb and Cu levels were below regulatory limits and Cd undetected in water columns, their average concentration exceedances were between 32 and 70 times higher in the biofilms. Results question the assignment of water potable based on regulatory standards alone.

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Introduction

Biofilms are consortium of microorganisms which form on solid surfaces in aqueous or wet environments (Costerton et al. 1994). They could be found in surface and ground waters, in drinking water piping and wastewater treatment plants, and on other technical equipment such as in the medical field (Wanner and Bauchrowitz, 2006). Biofilms execute a niche and so, interact strongly with their environment; are greatly affected by, as well as in return, affect the physical and chemical conditions in their enmeshing habitats.

Biofilms prefer to live in sessile communities (Flemming and Wingender, 2001) and include bacteria, algae, amoebas, ciliates and fungi in a great variety of compositions. Sunlight favours the growth of photoautotrophic components of biofilms such as algae and cyanobacteria and they conduct photosynthesis and thus, build up their biomass from inorganic substances. By this function therefore, these autotrophs are primal species in the trophic chain. However, in the absence of sunlight, biofilms are formed mostly by heterotrophic bacteria, which degrade organic substances, with the less frequent chemoautotrophic bacteria which utilize inorganic substances (Wanner and Bauchrowitz, 2006). In streams, algae-dominant autotrophic biofilms are mostly found on the riverbed and bacterial-dominant heterotrophic biofilms are found in the pore systems under the river bed (Lock, 1993). As biomass producers and decomposers therefore, biofilms are important components in the trophic web.

In biofilms, microorganisms are embedded in a slimy matrix which consists of extracellular polymeric substances that are excreted by the organisms themselves. These polymeric substances contain mainly high-molecular polysaccharides, proteins, other carbohydrates (such as uronic acid), and small amounts of lipids and nucleic acids (Wanner and Bauchrowitz, 2006).

As microorganisms, biofilms have been particularly utilized as interesting models in ecotoxicology to estimate the pollutant loading of natural water bodies and the hazard potential of toxic substances. Their suitability for this purpose lies in the central role they play in ecosystem metabolism and interaction with toxic substances (Doering and Uehlinger, 2006), and on the other hand because, as immobile biological elements, they accumulate pollutants over a long period of time and may thus reveal chronic impacts (Wanner and Bauchrowitz, 2006). Examples of such pollutants are the trace metals (Pb, Cd, Cu, Zn, Al, etc), which are recalcitrant in the environment.

Though they are important trace nutrients for water organisms, they can also be toxic at elevated enough concentrations. An exploratory determination of levels of some trace elements of the Otamiri River, one of the major river systems in Owerri, the capital of Imo State, southeastern Nigeria revealed concentrations that were below permissible limits by regulatory bodies, or even undetected by analytical instruments used. However, even low metal concentrations can have negative impacts on water organisms as well as local consumers, especially when considered on the merit of their bioaccumulative potentials over a length of time. Unfortunately, current researches in this area have been concentrated on the comparison of concentrations with these regulatory standards as criteria for assigning the river water potable. This current research therefore investigated the accumulation potentials of some heavy metals of environmental and public health importance (Cu, Pb and Cd) in consortium of resident biofilms of Otamiri River against background levels in water columns. The study approaches are as follows:  - Determination of the concentrations of the trace elements in slide and natural biofilms of the river - Comparison of the concentrations of the trace elements in biofilms with water column levels as well as regulatory standards, and - Determination of spatial variation in trace metals concentrations in biofilms.

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Source : Trace metals accumulation in biofilms of the upper and middle reaches of Otamiri river in Owerri, Nigeria