Essay: Trace metals connected with  industrial discharge and agriculture activities

Rapid economic development and urbanization bring prosperity worldwide including Malaysia. However, recently, due to anthropogenic and nature activities could lead adverse environmental effects like species extinction, loss of  biodiversity, acid rains, global warming, climate change, hazardous waste disposal problems, frequent and intensive eco accidents are also on the rise. Although these problems are very important for the future of mankind, unfortunately, people have not realize that heavy metals pollution impacts on them directly through effects on their health through food supply pollution like fish (Alloway and Ayres, 1993; Hänninen et al., 2014). Therefore, using geochemical partitioning such as sequential extraction technique (SET) and in vitro digestion model are better ways to assess health risk of human consumption in order to improve ecological risk assessment and pollution control. These techniques provide substantial information to determine of the relative bioavailability, which can be obtained by determining the solubility of sediment and fish heavy metals in digestive juice and to determine of the absolute bioavailability, which refers to the fraction of heavy metals mobilized from sediment and fish to digestive juice, absorbed by the body and involved in the circulation system (Ruby et al., 1999). Although a direct aqua regia digestion methods have widely apply in different studies in potential risk assessments, it is still poor indicator of the actual hazard due to toxicity and bioaccumulation of metals are related to their mobility and chemical speciation (Gu et al., 2015; Madrid et al., 2008; Camusso and Gasparella, 2006). Bioaccessibility heavy metals depend primarily on heavy metal binding to sediment reactive surfaces and are controlled by sorption, complexation, and redox processes. In turn, each of these processes is largely controlled through the variability of soil properties, including pH, organic matter, and soil texture (Pelfrene et al., 2011; Rodrigues et al., 2013). This relationship makes it possible to predict the bioaccessibility of heavy metals from sediment into biota (Buchter et al., 1989; Ruby et al., 1999). In vitro digestion model has been extensively applied to study physiological changes, digestibility, and release of food components under simulated gastrointestinal conditions (Hur et al., 2011). In vitro digestion model is the best used in the determination of bioavailability of heavy metal in food since it mimics quite close to the physiological condition in human body. Previous studies that have been done using the digestion model can be a reference for a further study to study the bioavailability of heavy metal in fish. Limited studies have applied health risk assessment using in vitro digestion model output (bioavailability of heavy metal). Health risk assessment is essential to be included in the vitro digestion studies as a rapid indication of heavy metal contamination and potential human health indicator. To simulate the digestion process in the human gastrointestinal tract by simulated in a simplified manner by applying physiologically based on some parameters that influenced physiologically conditions such as gastric pH, intestinal pH, food constituents, residence time and particle size.
In recent year, the pollution of the surface sediments especially rivers with toxic metals has been attracting considerable public attention over the past few decades. Additionally, this ecosystem receives anthropogenic sources of metals owing to human activities such as industry, agriculture, mining, domestic sewage, boat activities and construction works for urban development. These can pose serious threat to the food chain system in the aquatic environment (Martin et al. 2015). Thus, these wastes are known to contain heavy metals which are known to be toxic, can bio-accumulate and are persistent in the environment. Sediments are important sinks for different pollutants like pesticides and heavy metals and also play a significant role in the remobilization of contaminants in aquatic systems under favourable conditions. (Ikem et al., 2003; Sow et al., 2013). Sediments are considered not only a vital sink of heavy metals proceeding to their discharge into aquatic environments but also an indicator of pollution history (Rodríguez-Barroso et al., 2010). A successful evaluation for mixed accumulation of heavy metals from natural and anthropogenic sources typically requires normalizing methods for distinguishing the two different sources (Idris, 2008). Geochemical normalization approaches such as the enrichment factor (EF) and geo-accumulation index (Igeo) methods have been commonly used for the purpose.  Fish can accumulate large amounts of heavy metals from the surrounding waters and sediment and uptake by fish species would be directly transferred to human populations via fish consumption. Heavy metal mobility or availability in contaminated materials depends upon the different chemical and mineralogical forms that occurred. Sediments provide habitats for many aquatic organisms and a major repository for heavy metals introduced into surface waters. Therefore, it is necessary looking into the relationship between heavy metals concentrations in sediment and in fish tissue which can be an advantage for identifying the effects of anthropogenic activities on the food chain in the Langat and Bernam Rivers. Therefore, analysis of Catfish (Arius maculates) would give a better answer on bioaccessibility and bioavailability of hazardous metal which is a concern due to this fish is a common menu locally and freshwater fish consumption provides an important source of protein requirements, abundant and easy to sample. The Langat and Bernam Rivers was focused because of no detailed study on this fish around these regions.
1.2 Problem statement
Langat and Bernam River basin are located in an economic strategic place in Malaysia that is important as agriculture area and as the largest source of water supply for the state of Selangor and Perak of Malaysia, especially for irrigation.  However, due to rapid urbanization within these regions and changes economic policies involved changes in land use activities which make the rivers more exposed to different pollution problems such as industrial and domestic sewage, agrochemicals (fertilizers and herbicides) used on agricultural lands, and sand mining (Santhi and Mustafa, 2013; Idrus et al., 2004; Yap and Ong, 1990), these are all likely to cause heavy metal pollution to the these rivers. These Rivers were chosen for the present study because of it is situated in the most urbanized and the most developed areas in Selangor and Perak, serving approximately 1.2 million populations living around Langat Basin and 107.77 thousand populations living around Bernam Basin. In addition, it provides water for industries and agriculture located along its banks. The lack of pollution control and discharge the pollution from both industries and economic activities directly and indirectly into the river which definitely affects the ecosystem and human health (Mokhtar et al., 2009a). In fact, using only the total metal content in determining potential risk assessments is a poor indicator of metals effect and does not give enough information about the released and toxicity of metals (Gu et al. 2015; Madrid et al. 2008; Camusso and Gasparella 2006). Thus, evaluating metal bioaccessibility by using in vitro digestion model would not only provide a rapid estimation of ecosystem quality but also be able to realistically assess the potential exposure risk to humans and biota (Ahmed et al., 2015). Therefore, overcome to this problem requires an understanding of some of the important characteristics, speciation, and effects of bioaccessibility metals released to the environment in human health.
1.3 Research Objectives
This is study was conducted to determine the concentration, distribution and bioaccessibility associated with trace metals connected with  industrial discharge and agriculture activities and to assess the overall classification of some metals as well as their risk status in catfish (Arius maculates) and surface sediments of Langat and Bernem  Rivers. The specific objectives of the study were:
1- To identify the spatial distribution and sources of heavy metal namely Hg, Cd, Cr, Ni, Sn and Fe concentrations in surface sediment from Langat and Bernam rivers by using multivariate techniques and pollution indices .
2- To determine the bioaccessibility of heavy metals in surface sediment from Langat and Bernam Rivers using sequential extraction technique (SET) and simple bioavailability extraction test (SBET).
3- To estimate and influence of physicochemical properties and chemical fractions of surface sediment on the bioaccessibility of heavy metals contaminant in Langat and Bernam Rivers
4- To evaluate bioaccumulation of heavy metal in different organs of catfish namely muscles, kidney and livers and their relationship with chemical fractions in surface sediment from Langat and Bernam Rivers.
5- To quantify concentrations of heavy metals in muscles of catfish in bioaccessible fraction obtained after an in vitro assay with estimated potential risk of heavy metals consumption.
4.1 Significance of Study
Bioaccessibility and bioavailability data are of great importance to the health risk assessment of trace elements in sediment and fish. There was cap on the bioaccessibility of trace elements in sediment and fish tissue in Langat and Bernam Rivers. Using sequential extraction techniques (SET) would give results in selective of metals that are associated with non-resistance form (anthropogenic) and resistance form (natural). Therefore, this technic can help to known the sources of pollution from the location. Bioaccessibility data are clearly an additional tool toward furthering our understanding of human health risk at contaminated sites and have the potential to act as a pragmatic decision-support tool. Thus, it important to investigate the dominant factors which may influence bioaccessibility of heavy metals in the prospect from one region to another and then improve health risk assessment and control pollution through developed predicting models varied in Langat and Bernam Rivers locations. Using comparative between different types of an in vitro digestion model (IVG and SBET) is also important through incorporating these methods to predict the bioaccessibility of heavy metals in the fish samples based on chemicals fractions. Thus, this information will assist ongoing exposure assessments considering the health risks of metal contamination in the Catfish. Therefore, The results can be useful as a baseline data for government bodies to adopt corrective measure on the issues related to heavy metals pollution in Langat and Bernam river in the future.