Abstract
BackgroundLevels of toxic metal exposure in indigenous inhabitants are key bioindicators of the severity of environmental contamination. This study measured the seasonal variation of heavy metals and metallothionein (MT) contents in Asian swamp eels (Monopterus albus) from a paddy field situated in Tumpat, Kelantan, Malaysia, to identify prevalence, patterns and associations and togain insight on the suitability of MT as a biomarker for metal exposure.MethodsGill, muscle and liver tissues of M. albus (n = 50) sampled during the ploughing, seedling, growing and harvesting phases of rice growing were collected. The concentrations of copper (Cu), zinc (Zn), lead (Pb), nickel (Ni), and cadmium (Cd) in these tissues were determined by flame atomic absorption spectrometry. MT from each sample was isolated and purified, and subsequently quantitated using UV spectrophotometry. Associations between metal and MT concentrations, season and tissue type were evaluated using Pearson correlation and ANOVA with post-hoc Tukey HSD analysis.ResultsZn was present in higher quantities in gill and liver tissues, while Cu levels were elevated solely in liver. Patterns of non-essential metal accumulation were varied: Cd was detected in low concentrations in all tissues, while Pb and Ni were abundant in gill tissues across all seasons. MT concentration in liver tissue was consistently higher than that found in muscle or gill tissue, except during the growing phase. Moreover, significant correlations (P < 0.05) were observed for Cd, Ni, and Zn when MT was employed as metal exposure biomarker. However, no significant association was found between high Pb and Ni levels and MT concentration in gill tissue.Variation of bioaccumulation rates of heavy metals among the different tissues was observed. Some of these metal concentration differences were found to be associated with MT concentration and, by extension, to its high metal-binding capacity.ConclusionsSignificant liver MT-Zn, MT-Cd, and MT-Ni correlations found in this study emphasised the role of metallothionein as a biomarker for exposure of zinc, cadmium and nickel metals in M. albus.
Highlights
Levels of toxic metal exposure in indigenous inhabitants are key bioindicators of the severity of environmental contamination
Monopterus albus, which is known as Asian swamp eel, refers to a kind of fish that lives in freshwater, in paddy fields
As for the Asian swamp eels that dwell in paddy fields, they have been exposed to various pollutants due to vast agrochemical usage of pesticides, fertilisers, herbicides, and polluted water
Summary
Levels of toxic metal exposure in indigenous inhabitants are key bioindicators of the severity of environmental contamination. As for the Asian swamp eels that dwell in paddy fields, they have been exposed to various pollutants due to vast agrochemical usage of pesticides, fertilisers, herbicides, and polluted water. Fish uptakes important micronutrients, such as Zn, Cu, Pb, Cd, and Hg, for metabolism functions from its diet or surrounding (sediments and water), which will eventually accumulate in tissues [3,4,5]. This suggests that high accumulation of metals in tissues may turn into harmful toxic, for example, the high levels of Cu and Zn discovered by Pipe et al [6] in fish tissues
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