*3.3.1.2. Sampling collection*

**Figure 6.** Acute toxicity of Ti, Zr, Cd, Cr, and Sb for *Daphnia magna*.

**3.3. Field test: bioaccumulation**

72 Water Quality

*3.3.1. Materials and methods*

60CSx—Garmin [74].

*3.3.1.1. Studied area characterization*

aquatic organisms, especially for fish and planktonic crustaceans.

The surface water quality norms require specific limits only for few very toxic and toxic metals. For example, Ti, Zr, Cd, and Pb norms are not established by the National Plan of River Basin Management—Annex 6.1.3B, despite of their acute toxic effects at very low concentrations (**Table 4**). Also the Directive 2008/105/EC on environmental quality standards in the field of water policy sets limits only for Ni, Cd, and Pb. The present limits assure the protection of

In order to assess the impact of metals in the field, the following sections present some preliminary data concerning the metal bioaccumulation into benthic invertebrates (mollusks).

The studied area was focused on a highly sinuous channel, located on the southeast area of the Danube Delta (Sf. Gheorghe Branch) receiving 22% of Danube's water flow. The Sf. Gheorghe Branch has a width varying between 150 and 550 m, and the water depth varies between 3 and 27 m. The sampling sites location was selected taking into consideration the changes in the Sf. Gheorghe Branch morphology as a result of the pressure from anthropic and environmental factors. Iron Gates I dam construction on Danube River led to a 10% decrease in the suspended sediment amount at Isaccea station. Moreover, the Iron Gates II dam building induced a 50% decrease in suspended sediment at Isaccea. These constructions alongside meander modification (during the years 1984–1988) have produced major changes in sediment distribution. The establishing of space location was performed using GPS type system map The sediment samples for both benthic invertebrates and metal analysis were collected in two replicates using a Van Veen grab, according to the following methodologies: EN ISO 5667‐1:2008, ISO SR 5667‐6:2009, SR ISO 5667‐12:2001 and EN ISO 9391:2000. Surface sample unit was of 255 cm2 , and the sampling depth was of 10 cm. The analysis of benthic invertebrates was performed according to SR EN ISO 8689‐1:2003. The species identification was performed using a Motic stereomicroscope. The results were calculated taking into consideration the wet biomass.
