Assessment of heavy metals found in commonly consumed fishes from Lake Lanao, Philippines

This study was carried out to assess potential heavy metal contamination in the muscles of three commonly consumed fish species in Lake Lanao and to determine associated health risks that may endanger local community residents who consume these fishes. The concentrations of Arsenic (As), Cadmium (Cd), Chromium (Cr), Mercury (Hg) and Lead (Pb) were assessed in the muscles of Glossogobius giurus, Oreochromis niloticus and Giuris margaritacea and were measured via atomic absorption spectrophotometry. Statistical analysis showed that heavy metal concentrations in the muscles of the three fish species collected from the two different locations in the lake are not significantly different (P>0.05) except for O. niloticus. Recorded amounts of the five heavy metals in the present study were lower than the maximum and standard levels except for Pb. Four (As, Cd, Cr, and Hg) among the five pollutants of concern obtained Non-carcinogenic Hazard Quotient (NHQ) values that are less than one, while NHQ values for Pb range between 815.6 and 1396.03 for all fish samples obtained from both sampling stations. The continued consumption of G. giuris, O. niloticus and G. margaritacea collected from Marawi City and Tugaya, Lanao del Sur posed a high likelihood for local residents to contract adverse non-carcinogenic impacts, specifically by Pb. This does not necessarily hold true for the whole of Lake Lanao however, due to limitations related to representativeness. Steps should be taken to manage the risks posed by the consumption of G. giuris, O. niloticus, and G. margaritacea from Marawi City and Tugaya, Lanao del Sur, especially in consideration of vulnerable groups such as children, pregnant women and their developing fetus, and people with existing health conditions. 2 Jalova Jr. et al. 2021 The Israeli Journal of Aquaculture – Bamidgeh • IJA.73.2021.1426167 Introduction Lakes are essential to human well-being. They provide a wide range of ecosystem services including flood control, biodiversity, climate change mitigation, river flow regulation, hydropower supply, as well as water purification and storage. In recent decades, emerging global threats closely linked to anthropogenic pressures such as land-use intensification, nutrient enrichment, hydrological modification, aquaculture and fisheries, climate change, and water depletion have been driving forces of changes in lakes and reservoirs. These pressures have caused habitat loss and degradation, eutrophication and pollution, food web alteration, and physical degradation in many inland bodies. Another emerging threat to lake sustainability is the ever-increasing number of emerging contaminants brought about by technological advances which add more waste products and chemicals into the environment. These contaminants are new compounds with little environmental regulation and whose impacts are still not completely clear. They range from personal care products and illicit drugs to endocrine disrupting compounds, which can pose a serious threat to both aquatic ecosystems and human health. Additionally, the presence of micro-plastics and anti-microbial resistance in lakes are increasing because of the widespread use of these products. Agriculture, aquaculture, and livelihood development caused a higher level of antimicrobial resistance in surface water systems, consequently, causing health problems to water users (Ho and Goethals, 2019). Fishing, being one of the most important ecosystem services provided by inland aquatic ecosystems, contributes significantly in meeting the basic human need for food. With the increasing world population, fish consumption meets the demand for food among lakeshore communities while also serving as a substitute for beef, pork and another animal protein (Béné et al. 2015). Lake Lanao is the largest lake in Mindanao with a total area of 347 sq km and is considered as one of the 17 ancient lakes on earth. Known as a pre-historic and socioculturally significant lake, Lake Lanao shelters a great biodiversity of aquatic life forms. Through the years however, the lake has not been spared from various anthropogenic activities associated with the growing demand of the lake’s resources—the water for domestic and agricultural use and hydro-power generation, contact recreation, boating, laundry and bathing, ritual use, water sports, fishes for domestic consumption and livelihood—among other numerous related uses. (Angagao et al., 2017). Heavy metals are metallic chemical elements that occur as natural constituents of the earth’s crust. They are toxic even at low concentrations and are considered as persistent environmental pollutants since they cannot be degraded or destroyed. As trace elements, some heavy metals are essential to maintain the metabolism of the human body. However, these can lead to poisoning at higher concentrations. Their toxicity depends on several factors including the dose, route of exposure, chemical species, as well as the age, gender, genetics, and nutritional status of exposed individuals (Tchounwou et al., 2012). The bio-toxic effects associated with heavy metals poisoning (cadmium, lead, arsenic, mercury, zinc, copper and aluminum) have the following general signs: gastrointestinal (GI) disorders, diarrhea, stomatitis, tremor, hemoglobinuria (condition causing a rust–red color to stool), ataxia, paralysis, vomiting and convulsion, depression, and pneumonia when volatile vapors and fumes are inhaled (Duruibe et al., 2007; McCluggage, 1991). The nature of effects could be toxic (acute, chronic or sub-chronic), neurotoxic, carcinogenic, mutagenic or teratogenic. The dangers associated with human consumption of potentially contaminated fishes could be averted with the application of scientific inquiries that are appropriate and timely. This study sought to assess potential risks to public health, the results of which will also serve to inform and forewarn the Meranao lakeshore communities and their respective local governments about the possible contamination of fishery resources in Lake Lanao. The study was limited on the determination of heavy metal concentrations in three commonly consumed fishes sourced in Lake Lanao. The findings were compared against the recommended standard and maximum levels allowed in fishes and other foods. Furthermore, health risks were evaluated only in consideration of human consumption of fishes which are potentially contaminated with As, Cd, Cr, Hg, and Pb. Assessment of heavy metals 3 The Israeli Journal of Aquaculture – Bamidgeh • IJA.73.2021.1426167 Materials and Methods Study site The study was conducted in two sampling sites—first of which is the lakeshore of Marawi City an urban community and known as the center of trade, commerce, and industry in the province of Lanao del Sur (Figure 1). The first sampling site/station is located proximate to the most affected area during the Marawi armed conflict that occurred in 1997 instigated by ISIS-inspired rebels. This point is also located nearest to the source or headwaters of the Agus river. The second sampling site/station is located in the lakeshore of the Municipality of Tugaya, which is about 26.3 km from Marawi City. Tugaya is known for manufacturing traditional Maranao arts and crafts, such as back-strap loom weaving, tapestry weaving, and other kinds of handmade textile manufacture; foundry casting of various forms of brass or bronze vessels, instruments, and decorative items; wood-carving and mother-of-pearl inlay work; metalwork and silverand gold-smiting. Collection of samples Commonly consumed fish species (10-15 individuals of each species) namely, Kadurog (Glossobius giuris; average weight 0.13 ± 0.07 kg and average length 192.0 ± 44.2 cm), Nile tilapia (Oreochromis niloticus; 0.30 ± 0.17 kg and 195.6 ± 47.1 cm) and Katolong (Giuris margaritacea; 0.034 ± 0.011 kg and 112.4 ± 12.6 cm) were collected from three sub-stations located in each of the two sampling stations. Fish samples were transported to the laboratory in boxes filled with ice. The mean length and weight of the fish were recorded. All fish samples were kept at low temperature until analysis (Öztürk et al., 2009). The fish samples were thoroughly washed with distilled water to remove any adhering contaminants, and they were put on a dissection tray and thawed at room temperature. They were dissected using a knife and forceps, and the intestine, guts and bones were removed. Muscle tissues of fish (dorsal and ventral muscle) were used in this study since it is the most edible part of the fish (Listrat et al., 2016). All the samples were immediately transported to a competent and duly-accredited laboratory for the processing of the samples and determination of heavy metals. Sample preparation Muscle portion was put in a clean Petri dish and dried in an oven at 120 ± 2oC for 48 hours through which a constant weight was obtained. Before acid digestion, the dried muscle was pulverized to a fine powder using a mortar and pestle and stored in a freezer (-4oC) prior to analysis. One gram of each sample (powder) was mixed with 20 ml distilled water and diluted using HNO3 (55%) and HClO4 (70%) mixed concentration in 100 ml Erlenmeyer flask on a heating digester (200 to 250°C) until a clear solution was obtained and the volume was reduced to approximately 15 ml. This solution was then filtered using Whatman no. 1 filter paper into the volumetric flask and diluted to 50 ml. The prepared samples were analyzed using Atomic Absorption Spectrophotometer (Perkin Elmer Inc.). Data analysis and comparison Descriptive statistics such as average and standard deviation values were calculated. Finally, the mean concentration of heavy metals found in the different fish samples were compared to the recommended accepted value provided by FAO/WHO to check if the present value of heavy metals are within the standard and tolerable limits or not. Health risk assessment The health risks associated with ingesting A