Evaluation of potential ecological risk and contamination assessment of heavy metals in sediment samples using different environmental quality indices a case study in Agusan River, Caraga Philippines
The contamination and potential ecological risk posed by heavy metals from thirteen (13) sediment samples from different sampling sites along the lower portion of Agusan River were analyzed and assessed using different pollution indices. The results obtained shows that the total digest concentrations of different heavy metals under investigation have the following order: Cd Pb Zn Mn, for both first sampling periods. The speciation and distribution pattern have shown that significant amounts of all metals are present in the residual fraction. Similarly, oxide bound and organic bound fractions were found to be highly important for Zn and Mn while Cd and Pb were significantly associated in the residual and exchangeable fractions. The results of different pollution indices moreover, showed that among all the heavy metals being studied, Cd posed the highest environmental risk across all sampling stations in both sampling periods and Mn metal was highly enriched and abundant in all of the sampling stations. Importantly, PCA results suggest that Zn, Mn and Pb may have the same origin while Cd might be coming from different sources, and this is corroborated well with the cluster analysis results. The results obtained from this work provide baseline data on the assessment of heavy metal pollution in the lower portion of Agusan River. Importantly, the acquired environmental indices will certainly help safety managers in assessing and interpreting the potential risk of the sediment associated chemical status that might adversely affect aquatic organisms in the selected sampling sites. *Corresponding Author: Rey Y. Capangpangan reycapangpangan@gmail.com Journal of Biodiversity and Environmental Sciences (JBES) ISSN: 2220 6663 (Print) 2222 3045 (Online) Vol. 8, No. 1, p. 1 16, 2016 http:/www.innspub.net J. Bio. Env. Sci. 2016 2 Capangpangan et al. Introduction The growing global concern about heavy metal contamination and environmental pollution has prompted the scientific community to do extensive research to address this problem (Zerbe et al. 1999, Abdallah 2012, Zhao et al. 2012, Vega and Weng 2013, Aktaruzzaman et al. 2014, Zhuang and Gao 2014, Xu et al. 2015) Human activities, as a result of rapid industrialization and economic development have resulted to a rapid discharged of different heavy metals in various point sources (Wang et al. 2011, Yuan et al. 2013) Most of these heavy metals were reported to be indestructible and have toxic effects on living organisms, especially when the permissible limits were exceeded (MacFarlane and Burchett 2000, Ekeanyanwu et al. 2011, Jayaprabha et al. 2014. As being known, heavy metals from different anthropogenic sources will be transported thru various processes and being deposited in the aquatic sediments. Studies have shown that metal ions often have a strong tendency to associate in the particulate matter in the water column and may exists in different forms which dictates their reactivity and toxicity (Tessier and Campbell 1987, Ideriah et al. 2012) Hence, the study on the speciation pattern of these heavy metals call for a special attention and was considered as one of the important research areas in environmental studies. Furthermore, establishing considerable evaluation measures in terms of the possible contamination and potential ecological risks posed by different heavy metals based on different environmental quality indices is of paramount importance. Certainly, these evaluation measures is of significant help for development, evaluation and converging raw environmental data to decision makers and managers for public interest (Caeiro et al. 2005, Qingjie et al. 2008) Accumulation of metal contaminants in sediments can pose serious environmental problems to the surrounding areas (Zakir et al. 2008, Kumar and Patterson Edward 2009, Ong and Kamaruzzaman 2009, Wang et al. 2010) Trace metal contamination in sediment matrices have been reported to affect the water quality and the likelihood of bioaccumulation into aquatic organisms, resulting in potential longterm implications on human health and ecosystems (Fernandes et al. 2007, Li et al. 2012, Abdel Baki et al. 2013. However, the total metal concentration provides a poor indication of environmental risk since this information is not sufficient in understanding their chemical behavior. More often than not, trace metals undergo numerous changes in their speciation during their transport due to dissolution, precipitation, sorption and complexation phenomena (Akcay et al. 2003, Odukoya and Abimbola 2010) This study presents a baseline data on the assessment of heavy metal pollution in the lower portion of Agusan River, Caraga Philippines. As of this writing, there has no documented report which deals into specific investigation on the speciation of heavy metals in sediment samples which is a significant factor in the transport of heavy metals in the chosen study sites. The extent of heavy metal pollution in Agusan River has great impacts on the different settlements along the area. Thus, the main purpose of this work was to demonstrate and evaluate different environmental indices (multi element indices) derived from total content based and speciationbased indices in interpreting the potential risks posed by heavy metals in the chosen sampling sites. Materials and methods Description of the Sampling Sites Agusan River is the third largest basin of the Philippines (2008) It is also the draining majority of Caraga Region and some parts of Compostela Valley province with major gold mining and/or processing operations which can be considered as culprits of heavy metal pollution. Sediment samples were strategically collected in 13 chosen sampling sites which represent the whole lower portion of the river. Mostly, the selected sampling stations were chosen in areas with noted tributaries in the main river (Fig. 1) Likewise, these sites were characterized by some manufacturing J. Bio. Env. Sci. 2016 3 Capangpangan et al. industries, mixing factories with residence and with agricultural activities nearby. Moreover, mining industries upstream of the river were reported to be in operation that may contribute for the heavy metal load in the lower portion of the river. Exact locations for all sampling sites were determined using a global position system and entered into the geographical information system for processing. Fig. 1. Graphical representation of all the sampling sites in Agusan River. Sample collection and preparation About 1 kg of sediment samples were collected, stored in a polyethylene bottle/container and transferred to the laboratory for analysis. Sample treatment, extraction and subsequent analytical determinations are being performed in a clean laboratory and with acid washed glassware's. The sequential extraction method for the analysis of heavy metal speciation is being analyzed according to the outlined method. Quantitative amount of the heavy metal fraction and free heavy metal (total heavy metal content) were analyzed using the Atomic Absorption Spectroscopy (AAS) Total concentration of Mn, Zn, Cd and Pb Sediment samples were digested using a concentrated HNO3 and HCl (aqua regia) In brief, 20.0 mL aqua regia was added to 1.0 g of dry sediment sample and was digested for 3 hours. Then, about 20 mL of 0.08 M HNO3 was added and it was heated continuously to near dryness. The supernatant solution was then filtered and diluted to 50 mL with doubly deionized water. Chemical Fractionation A modified sequential chemical extraction protocol as described by previous literature (Tessier and Campbell 1987) was employed in this study for the determination of the different operationally defined metal fractions (Fig. 2) All reagents were prepared from reagent grade chemicals and doublydeionized water. Similarly, triplicate trials were performed in all of the analyses. Environmental quality indices Quantitative interpretation on the potential impacts of different metal ions is an integral part as far environmental assessment is concerned. Various J. Bio. Env. Sci. 2016 4 Capangpangan et al. pollution calculation methods were usually used in order to assess the heavy metal enrichment and the degree of contamination in sediments and other biota. In this particular study, eleven (11) different environmental quality indices were applied to assess the level of contamination of the four (4) sedimentassociated metals in the lower portion of Butuan River. These indices covered the speciation/total content and individual and multi element approaches. Calculations of these indices were adopted from these reported literatures (Muller 1969, Buat Menard et al. 1979, Hakanson 1980, Perin et al. 1985, Ikem et al. 2003, Priju et al. 2006, Qingjie et al. 2008, Yaqin et al. 2008, Rabee et al. 2011, Varol 2011, Zhao et al. 2012, Banu et al. 2013, Nwankwoala 2013, Asrari 2014, Aktaruzzaman et al. 2014, Zhuang and Gao 2014) Results and discussion Small and coarse particles were observed to be present in all of the sediment samples. The sediment particle sizes were monitored by sieving it using 0.850 mm mesh sieve. It has also been observed that some samples were made up of sand particles, as expected, due to deposition of siliceous sand derived from long shore water current. As noted, sediments are generally the sinks for metals in aquatic environment and constitute in an enriched metal aquatic environment and comprises an enriched metal pool that can be potentially accumulated by the benthic animals (Campbell et al. 1988) Fig. 2. Schamatic diagram showing the.extraction and fractionation process. Total digest concentrations of Cd, Pb, Zn and Mn The total digest concentration of all metals (Cd, Pb, Zn and Mn) expressed in mg/kg is graphically represented in Fig. 3. As shown, the total digest concentrations of Cd across all sampling stations are almost comparable which ranges from 0.622 to 2.44 mg/kg and 0.733 to 2.48 mg/kg