Toxic metals biomonitoring based on prey-predator interactions and environmental forensics techniques: A study at the Romanian-Ukraine cross border of the Black Sea

Preliminary investigation of lower Danube pollution caused by potentially toxic metals

The current study aims to assess the pollution status of the European river-sea system lower Danube River-Danube Delta-North West Black Sea, through an integrated analysis of metal concentrations in water, sediments and fish community. The Danube flows through numerous industrial cities and receives a significant amount of pollutants due to the reception of urban and industrial emissaries, as well as agricultural land runoff. Samples of water, sediments and fish (10 species) were collected from 7 representative sites along Danube River, Danube Delta and Black Sea shore. For the analysed fish species, potentially toxic and essential elements (Pb, Cd, As, Cu, Fe, Zn, Mg, Ca, Na, K) from muscle and liver samples were measured and discussed. Measurement of elements and other environmental quality parameters were determined for water and sediments. The Black Sea area, represented by S6 and S7, received sediments from Danube with the lowest concentrations of Cd (0.05 ± 0.01 μg g^-1, respectively 0.01 ± 0.001 μg g^-1), Pb (3 ± 0.03 μg g^-1, respectively 2 ± 0.03 μg g^-1), As (2 ± 0.02 μg g^-1, respectively 1.4 ± 0.3 μg g^-1), Ni (8.9 ± 0.1 μg g^-1, respectively 5.2 ± 0.2 μg g^-1), Cr (8 ± 0.7 μg g^-1, respectively 5 ± 0.2 μg g^-1), Cu (3 ± 0.1 μg g^-1, respectively 2 ± 0.04 μg g^-1), Fe(6 ± 0.3 μg g^-1, respectively 3 ± 0.1 μg g^-1) and Zn (0.03 ± 0.003 μg g^-1, respectively 0.017 ± 0.001 μg g^-1). These results suggest that the Danube Delta system plays an important role in filtering the pollutants. Based on the biota and water analysis, there was no correlation observed between Cd, respectively Pb concentration in the environment and fish body (Person Coef. = -0.02 in muscle tissue and -0.01 in liver tissue, respectively Pearson Coeff. = -0.06 in muscle tissue and 0.1 in liver tissue). Cadmium remained an active element in the pollution of the Danube area (S1 and S2), with high concentration in the water matrix (0.14 ± 0.02 μg L^-1, respectively 0.05 ± 0.01 μg L^-1) and fish muscle (0.15 ± 0.03 μg g^-1f.w. in C. carpio - S2). This fact was confirmed by several other studies.

Antagonistic effects in zebrafish (Danio rerio) behavior and oxidative stress induced by toxic metals and deltamethrin acute exposure

In natural environments, the aquatic organisms are exposed to complex mixtures of chemicals which may originate from natural sources or from anthropogenic activities. In this context, the aim of the study was to assess the potential effects that might occur when aquatic organisms are simultaneously exposed to multiple chemicals. For that, we have studied the acute effects of cadmium (0.2 μg L^-1), nickel (10 μg L^-1) and deltamethrin (2 μg L^-1) as individual toxicants and as mixture on the behavioral responses, oxidative stress (SOD and GPx), body electrolytes and trace metals profiles of zebrafish (Danio rerio). So far the scientific literature did not report about the combined effects of pesticides and toxic metals on zebrafish behavior using a 3D tracking system. Compared with other studies, in the present paper we investigated the acute effects of two heavy metals associated with a pesticide on zebrafish, in the range of environmentally relevant concentrations. Thus, the environmental concentrations of cadmium and nickel in three rivers affected by urban activities and one river with protected areas as background control were measured. The observations that resulted in our study demonstrated that deltamethrin toxicity was significantly decreased in some of the behavioral variables and oxidative stress when combined with CdNi mixture. Consequently, our study supports previous works concerning the combined toxicity of environmental chemicals since their simultaneous presence in the aqueous environment may lead to higher or lower toxicological effects on biota than those reported from a single pollutant. Therefore, the evaluation of toxic effects of a single contaminant does not offer a realistic estimate of its impact against aqueous ecosystems. This study also supports the idea that the interactions between different chemical compounds which do not exceed the maximum permitted limits in environment may have benefits for aquatic life forms or be more toxic.

Patterns of toxic metals bioaccumulation in a cross-border freshwater reservoir

In freshwater ecosystems toxic metals can follow different routes of bioaccumulation in the organisms' body mass, routes that are similar to electronic circuits, but far more complex due to their hierarchy levels. Reservoirs located on river courses have positive impacts on economic and social development because they concentrate large water volumes used for electrical energy production, water supply, irrigation, industry, aquaculture, providing ecosystems for migratory birds and aquatic species. The aim of the study was to assess the contamination with copper (Cu), cadmium (Cd), lead (Pb), chromium (Cr) and nickel (Ni) of a cross-border reservoir located on River Prut (border between Romania and Republic of Moldova) in a temperate climate zone. Several aspects were considered: seasonal variation of water parameters and toxic metals, bioconcentration in eight fish species and transfer from prey to predator through the food chain, bioaccumulation by two freshwater molluscs separated in size groups and their role as bioindicators of toxic metals pollution. Metals concentrations were measured with an atomic absorption spectrometer (HR-CS GF-AAS). Cadmium, lead, nickel and chromium concentrations limits in water samples were below the detection limits (0.005 μg L^-1Cd, 0.013 μg L^-1Pb and 0.011 μg L^-1Cr) during the monitoring period, suggesting that anthropogenic contamination was insignificant in the studied ecosystem. Fish liver and kidney had specific selectivity for copper (0.9-55.56 μg g^-1) and cadmium (0.097-1.031 μg g^-1) in case of pike-perch and bighead carp. The separation of molluscs in size groups did not prove that toxic metals increase in concentration with the organism age.