Trizinc bis(orthophosphate)

Sediment toxicity

Description of key information

A quality-screened database on the toxicity of zinc towards freshwater and marine sediment-dwelling organisms has been compiled from the Zn RAR (2008) and updated with newly retrieved literature data (search 1995-2021). Evaluation of the study quality followed the Klimisch scoring system, and only the toxicity data that received a Klimisch score of 1 or 2 were considered relevant for the derivation of the Predicted No Effect Concentration (PNEC) . Chronic NOEC/EC10 values based on measured Zn concentrations for ecologically relevant endpoints for risk assessment purposes (i.e. survival, growth or reproduction) were retained. The available database of chronic freshwater sediment toxicity tests for zinc provides information on seven different species (single-species exposures) and two long-term field colonization studies.

 

Chronic toxicity test results for the freshwater compartment are available for the following sediment-dwelling organisms representing different feeding habits and life strategies i.e. the amphipods Hyalella azteca and Gammarus pulex, the oligochaetes Tubifex tubifex and Lumbriculus variegatus, the insect Chironomus dilutus, Epheron virgo and Hexagenia. For the marine compartment an additional test result is available for the amphipod Melita plumulosa .

 

Since several data for different taxonomic groups are available, the ‘PNEC sediment’ was calculated using a statistical extrapolation method, and a species sensitivity distribution curve (SSD) was constructed both on the freshwater data set and on the pooled freshwater/marine dataset. The PNEC sediment was derived  from the median Hazardous Concentration (5th percentile) of the SSD.  As zinc toxicity in sediments is mitigated by the presence of Acid Volatile Sulfides (AVS) and organic carbon (OC), only the chronic toxicity data obtained under conditions of low OC concentrations and low-to-median AVS concentrations in the sediment were used (i.e maximizing bioava. Further analysis showed that there is no need for applying an additional assessment factor on the derived HC5-50 value due to the conservative nature of the assessment. Consequently, the PNEC is set at the level of the median HC5 value, which is considered as protective for EU freshwater ecosystems resulting in a PNEC sediment of 146.9 mg/kg dry wt. for the freshwater compartment and PNEC sediment of 162.2 mg/kg dry wt.  for the marine sediment compartment.

Additional information

In the  the overview is given of all chronic values that are available. The  underlined values have finally been used and used as input values for the SSD for deriving the 5^th percentile as a basis for the derivation of the PNEC sediment. Please note that data were not aggregated if several EC10/NOEC values were available because not all tested sediments were worst case sediments. The hexagenia datapoint was omitted from the analysis because the sediment was not a realistic worst case sediment leaving 6 EC₁₀/NOEC values for six species. Including this data point would result in a higher HC5 value (results not shown). This example highlights again that only data obtained under the most conservative sediment conditions, were used for the SSD.

 

Table 1: Summary of chronic values (those underlined and in bold) that were used as input values for the SSD for deriving the 5th percentile values as a basis for the PNEC freshwater sediment.

 

Taxonomic group	Species	Endpoint	Species EC10/NOEC	Remark
Crustaceans	Gammarus pulex Hyalella azteca	growth growth	218 250	NOEC EC10
Insects	Ephoron virgo Chironomus dilutus Hexagenia	mortality growth growth	231.4 521.6 713	EC10 EC10 EC10
Oligochaetes	Lumbriculus variegatus Tubifex tubifex	growth reproduction	878 1101	EC10 NOEC

Only one EC10 value for the marine amphipod Melita plumulosa was  deemed appropriate  to be included (Table 2).

 

Table 2: Species EC-10 values (total Zn) for the most sensitive endpoint for all sediment dwelling organisms

Taxonomic group	Species	Endpoint	Species EC10/NOEC	Remark
Crustaceans	Melita plumulosa	reproduction	753.6	EC10

If the long term marine and freshwater sediments effect data are pooled a sediment effects dataset of seven EC₁₀/NOEC values for seven different species is available for zinc for the sediment compartment (Table 3).

 

Table 3: Species EC₁₀-NOEC values (total Zn) for the most sensitive endpoint for all sediment dwelling organisms (marine and freshwater data pooled; only those underlined and in bold were used in the SSD)

Taxonomic group	Species	Endpoint	Species EC10/NOEC	Remark
Crustaceans	Gammarus pulex Hyalella azteca Melita plumulosa	growth growth reproduction	218 250 753.6	NOEC EC10 EC10
Insects	Ephoron virgo Chironomus dilutus Hexagenia	mortality growth growth	231.4 521.6 713	EC10 EC10 EC10
Oligochaetes	Lumbriculus variegatus Tubifex tubifex	growth reproduction	878 1101	EC10 NOEC

 

For more information, see the background document on environmental risk assessment of zinc in sediment, attached to section 13 of IUCLID.