Variability of sediment-contact tests in freshwater sediments with low-level anthropogenic contamination – Determination of toxicity thresholds

Sediment contact tests as a tool for the assessment of sediment quality in German waters

“…Suitable toxicity thresholds had been defined for all test systems and calculated on the basis of the minimal detectable difference and the maximal tolerable inhibition as described by Höss et al [22] during the joint research project SeKT [24,25]. In the following, inhibitory effects that exceeded the respective toxicity thresholds were defined as toxic effects.…”

“…In the following, inhibitory effects that exceeded the respective toxicity thresholds were defined as toxic effects. In the plant test, a lightly contaminated native sediment (from the Rhine River) was used as the negative control, instead of the artificial control sediment that was used in former studies [21,22]. Therefore the minimal detectable difference (10%) and maximal tolerable inhibition (21%) had to be recalculated, which had, however, no influence on the toxicity threshold of 20%.…”

“…In the United States and Canada, macroinvertebrates have mostly been used for whole sediment toxicity testing [10][11][12]; standardized sediment contact tests (SCTs) with organisms from other trophic levels did not exist until recently. However, within the last two decades, new SCTs have been developed in Europe using a broader range of organisms, such as bacteria [13][14][15], yeast [16], nematodes [17,18], fish embryos [19,20], and macrophytes [21], with some of them being standardized (ISO 10872; ISO/DIS 16191; ISO/DIS 10871) and approved for assessing the toxicity of contaminated freshwater sediments [22,23].…”

“…The response of a test organism to these sediment properties can lead to variability in the toxicity endpoint that might be interpreted as a toxic effect. Therefore, Höss et al [22] set up test-specific toxicity thresholds for a set of SCTs that consider the natural variability of each test system and toxicity endpoint, based on two criteria: (1) the power of a test to detect a significant difference to the control (measured as minimal detectable difference), and (2) the variability of the toxicity endpoint in lightly polluted sediments compared to the control sediment (measured as maximal tolerable inhibition). Thus, an inhibitory effect of a certain sediment sample is regarded as a toxic effect, if it exceeds the endpoint-specific toxicity threshold (expressed as percentage of inhibition).…”

“…The present study represents the second part of the SeKT project and applies the recommended battery of SCTs to classify the toxicity of polluted freshwater sediments from rivers and lakes, using the toxicity thresholds that were elaborated in the first part of the project [22]. The SCT-based classification was compared with sediment quality guidelines (SQGs) that are derived from chemical data and often used to describe the toxic potential of sediments [26,27].…”