**4. Conclusions**

All the biota sediment bioaccumulation factors were subunitary, which indicated a slowly

Risk characterization is required for all chemicals as an estimation of their exposure and adverse effects on the environmental compartment. Generally, this is based on Predicted Environmental Concentration (PEC) and Predicted No Effect Concentration (PNEC) calcula‐

In order to estimate the current contamination of Danube surface water and sediment with metals, we use the average of the measured environmental concentrations (MEC) as PEC values, for the period 2009–2013 at Murighiol and Uzlina. The PNEC value calculation was made using an assessment factor (AF) of 1000 applied for acute toxicity values—LC50 (96 h) or 10 applied for chronic toxicity values—MATC for *C. carpio* (our laboratory tests), which expresses the degree of uncertainty in the actual environmental extrapolation [87]. The risk quotients (RQs) between MEC values and acute or chronic PNECs were calculated, and the level of risk was expressed as: insignificant risk (RQs <0.1); low risk (RQs <1); moderate risk (RQs <10), and high risk (RQs >10). The estimated RQs for the most detected metals in Danube

water and sediment (Ni, Cd, Cr, Cu, Pb, and Zn) were summarized in **Table 9**.

**Metal MEC (µg/L)\* PNEC (µg/L) RQs acute Risk level RQs chronic Risk level S7 S8 Acute (AF = 1000) Chronic (AF = 10) S7 S8 S7 S8**

**Ni** 12.4 2.60 65.8 10.0 0.18 0.03 L/I 1.24 0.26 L **Cd** 0.36 0.37 0.16 0.10 2.25 2.31 M 3.60 3.70 M **Cr** 5.38 3.52 120 100 0.04 0.02 I 0.05 0.04 I **Cu** 12.9 14.5 2.17 5.00 5.94 6.68 M 2.58 2.90 M **Pb** 2.15 2.17 30.1 100 0.07 0.07 I 0.02 0.02 I **As** 1.82 1.73 0.40 0.50 4.55 4.32 M 3.64 3.46 M **Zn** 9.58 8.15 12.2 60.0 0.78 0.66 L 0.16 0.14 L

**Ni** 30.8 39.3 65.8 10.0 0.46 0.59 L 3.08 3.93 M **Cd** 0.50 0.51 0.16 0.10 3.12 3.18 M 5.00 5.10 M **Cr** 31.6 29.2 120 100 0.26 0.24 L 0.32 0.29 L **Cu** 35.1 47.0 2.17 5.00 16.2 21.7 H 7.01 9.41 M **Pb** 22.3 21.3 30.1 100 0.74 0.70 L 0.22 0.21 L **As** 9.61 9.30 0.40 0.50 24.0 23.3 H 19.2 18.6 H **Zn** 88.5 96.9 12.23 60.0 7.23 7.92 M 1.48 1.62 M

\* Average of concentrations in period of 2009–2013; I—insignificant risk; L—low risk; M—moderate risk; H—high risk.

**Table 9.** Estimated acute and chronic RQs at Murighiol (S7) and Uzlina (S8) for *Cyprinus carpio*.

bioaccumulation process occurred in the studied aquatic ecosystems.

tion, in terms of exposure and assessment of effects [86].

**3.4. Preliminary risk assessment**

78 Water Quality

*Surface water*

*Sediment*

The topic of this chapter was based on the assessment of aquatic systems quality related to persistent metal pollution. The toxic metals are the most frequently detected pollutants in the aquatic environmental, and their effects identification are essential to protect the ecosystems integrity as well as human health. Metal pollution is a global problem; thus, the international regulations with regard to the water quality demand compliance with the quality standards in surface water, groundwater, and biota. The use of organisms (such as fish, crustacean, and mollusks) as bioindicators of metal pollution allowed us to obtain valuable information about the effects on the Romanian common species and to estimate the quality of their environment. The results from laboratory toxicity tests showed the highest concentration values that are not relevant for the detected metal concentrations into surface water, but the metals accidentally released and long‐term accumulation could create similar conditions to the results of applied tests. Cd, As, Cu, Zn, Pb, Ni, Zr, and Ti have a very toxic and toxic effects for *C. carpio* and could raise concerns because of its importance for human as a fishery resource. Benthic invertebrates' analysis of the bioaccumulation level varied between species, metals type, and sampling sites. The metal analysis in mollusks shell showed that the metals involved in the metabolic processes (Fe, Mn, Zn, Cu, and Mg) had greater storage capacity than the toxic one (Pb, Cd). In case of *V. viviparus* shell, the selectivity of the metal concentration was represented as follows: Fe > Mn > Zn > Cu > Pb > Co > Cd, while the shell of *A. cygnea* had a greater accumulation capacity for Cu, As, Cr, Zn compared to *Unio* sp. The bioaccumulation factors of metals in benthic organisms were subunitary, which indicated a slowly bioaccumulation process occurred in the studied aquatic ecosystems. This conclusion highlighted a bioaccumulation process that can increase the persistence of metals in the ecosystem, with a long‐term potential risk in trophic chain. The preliminary aquatic risk assessment calculated for *C. carpio* for the most detected metals both in water and in sediment (Ni, Cd, Cr, Cu, Pb, As, and Zn) revealed insignificant to moderate risk considering the metals measured environmental concentrations, acute and long‐term effects. The results highlighted a pessimistic view concerning the quality of aquatic ecosystem needed to support the carp survival. The concern is related to the constant presence of metal concentrations especially in sediments which is the principal food provider, leading to bioaccumulation processes and trophic chain transfer. Future studies have been initiated to understand the long‐term effects of metals in aquatic biota and to complete the aquatic risk assessment considering the abiotic factors.

### **Abbreviations:**


