Trace elements in aquatic environment. Origin, distribution, assessment and toxicity effect for the aquatic biota

Abstract

Trace elements contamination and accumulation in bottom sediment represents a risk to environment and aquatic biota. Their anthropogenic or natural discharge, extension and cumulation can cause large scale of ecological destructions. Bioaccumulation and biomagnification is capable of leading to toxic level of these chemical substances in fish and other fresh water organisms (benthos, zooplankton), even when the exposure is low. The fish contamination through trophic structure can cause serious consequences to human health.

The aim of the manuscript was to assemble and summarize the latest literature on the environmental and the aquatic biota effects of trace element contamination of bottom sediments. The article is also a review of new methods for trace elements elimination and their assessment to impact on aquatic organisms. Based on collected scientific publications in last 20 years the most common and important trace elements in aquatic ecosystem are Chromium, Arsenic, Mercury, Cadmium and Copper. These compounds are dangerous for living organisms and can disrupt their homeostasis as well as a cardiovascular, nervous and digestive system. Nowadays exist many instrumental methods, which are available to determine the trace element concentration such as PMF, INNA, BCR, XRF and bioassay. In searched studies the most preferred and used analyse of trace element concentration in aquatic bottom sediments is bioassay. This biological method is good complement to physical and chemical analyses in procedures of sediment quality assessment. Bioassay method can indicate sensitive response of planktonic organisms to various trace elements and provide information about the real risk to aquatic life.

Introduction

The contamination of aquatic ecosystem with a wide range of pollutants has become a matter of concern over the last few decades (Dirilgen, 2001; Vutukuru, 2005). A large part of human activity causes the production of waste mostly discharged in aquatic ecosystem (Salomons et al., 1987).

The important part of aquatic ecosystems are bottom sediments (Förstner and Salomons, 2010; Smal et al., 2015). The river bottom sediments are fundamental components of the river environment, which provide nutrients for living organisms and act as receptors of anthropogenic contaminants (Reis et al., 2010). Among the bottom sediments pollutants, a significant role is played by trace elements, which, given certain concentration and conditions, are characterised by toxicity towards living organisms, bond durability as well as the ability of activation at different stages of the food chain (Rosado et al., 2016a; Tarnawski and Baran, 2018) (Fig. 1).

Many recent studies carry out scientific analyses with elements that are classified as toxic metals (Ali et al., 2016; Alves et al., 2014). The main representatives include Ag, As, Cd, Cu, Cr, Hg, Ni, Pb, Z. These metals are largely concentrated in urban or industrial areas more than in natural environment (Stankovic et al., 2014). The most toxic and important elements used for chemical observation are Cu, Cd, Ni (Siebielec et al., 2015). The major metals those concentration is considerably higher in natural waters are K, Ca, Mg, Mn, Fe. Deficiencies of these essential nutrients can be destructive for biota like for human health as well (Martins et al., 2014) Some of them can produce severe toxicity effects when there is an excess in certain levels in water (El-Monsef and El-Badry, 2017).

Principally the most basic trace elements in widespread are considered Li, Be, B, Al, Co, V, Se, Sb, Sr, Sn, Ti occurred at trace or ultratrace level in the crust (with the exception of aluminium which is a major component) (Test Methods for Evaluating Solid Waste, 2007). They are usually included at parts-per-billion (ppb = µg L⁻¹) or at parts-per-trillion (ppt = ng L⁻¹) levels. In order to determine the ability of contaminants to migrate within the environment, particularly considering the inclusion of contaminants in biogeochemical cycles, it is necessary to assess the reactivity and mobility of those compounds (Farkas et al., 2007; Gao et al., 2018; Rosado et al., 2016a; Rosado et al., 2016b). The trace elements are easy dissolvable and exchangeable, considering their ability to activate from the solid state and migrate to the aquatic environment, where they become biologically available (Baran and Tarnawski, 2015; Sutherland and Tack, 2007) (Fig. 1).

The behaviour of trace elements in bottom sediments is controlled by many factors. Their distribution depends on physical-chemical interactions and equilibria, largely governed by pH, electric conductivity, oxidation state of the mineral components as a content of iron and manganese oxides and the redox conditions of the aquatic system (Singh et al., 2005). Some authors agree that trace elements accumulation within sediments depends directly on parameters such as pH, ionic strength, the type and concentration of inorganic and organic “ligands” plus the availability of adsorption surfaces such as clay minerals and organic matter (Cao et al., 2015; Fonseca et al., 2013; Martínez-Santos et al., 2015). However, the content and quality of organic matter play a very important role in the assessment of trace element behaviour in the aquatic environment (Derrien et al., 2017; Hristov et al., 2017; Smal et al., 2015; Smith et al., 2014; Yang et al., 2011) (Table 1).

The bottom sediments are able to accumulate organic matter with contaminants, brought to the river and channel with different kind of sewage (Chen M. and Chen F., 2017). A large number of biogeochemical processes are involved, influencing the fate of trace metals. Among these processes, the microbial degradation and decomposition of organic matter during early diagenesis leads to major changes in the redox conditions between the overlying oxic waters and the oxygen-depleted sediments (Leister and Baker, 1994). As a result of decomposition, organic matter may constitute a source biogenic compound, and as a result of transformations, it may have a significant effect on the mobility, bioavailability and toxicity of trace elements (Bai et al., 2018) (Table 1).

Sediment resuspension (natural or anthropogenic origin) can disturb the biogeochemistry of sediments and potentially favour the remobilisation of trace metals from sediment particles to the water column (Caetano et al., 2003; Cantwell et al., 2002; Saulnier and Mucci, 2000). Moreover the resuspension can impact ecosystems through direct and indirect effects on freshwater organisms and their interactions (M. Chen and Chen, 2017) also ecosystem structure and functioning (De Robertis et al., 2003; Horppila et al., 2009; Nurminen and Horppila, 2006). The aims of review were: (1) to highlight the toxicity of trace elements in bottom sediments as a pollutant to aquatic biota and environment, (2) to show the several methods for determining and assessing of trace elements.