Dipotassium [[N,N'-ethylenebis[N-(carboxylatomethyl)glycinato]](4-)-N,N',O,O',ON,ON']zincate(2-)

Long-term toxicity to aquatic invertebrates

Description of key information

A Daphnia magna reproduction test (semi-static, 21 d) of the test item EDTA-ZnK2 was conducted according to OECD 211 under GLP conditions. 
Test species was Daphnia magna STRAUS. Ten daphnids, held individually, were used per nominal test item concentration and control. At the start of the exposure the daphnids were less than 24 hours old. The study was carried out under semi-static conditions with medium exchange three times per week. Aim of the test was to assess the effects on the reproduction capacity and other test item-related effects or parameters such as the intrinsic rate of the natural increase, the number of broods with living juveniles, first appearance of living juveniles, occurrence of aborted eggs and stillborn juveniles, adult mortality, body length and dry weight of the parental daphnids.

The test item EDTA-ZnK2 is a white solid. The aqueous media were prepared dissolving 50 mg of test substance in 2-L of test medium and stirring for approximately 10 min at ambient temperature. The lower test concentrations were prepared by dilution of this stock solution. Before the dilution was performed, the stock solution was checked for complete dissolution of the test substance. Five test concentrations were prepared and tested nominal concentration rates 25 – 12.5 – 6.25 – 3.13 - 1.56 mg//L (separation factor 2.0).
The stock solutions were checked visually to ensure that the test substance was completely dissolved.
The test item concentrations of EDTA-ZnK2 were analytically verified via LC-MS three times during the test (once within a period of 7 days) in the fresh media at the start of an exposure-renewal interval (0 hours; on test days 0, 9 and 19) as well as in the old media at the end of an exposure-renewal interval (24 hours; on test days 2, 12 and 21) in all test item concentrations and in the control.
The environmental conditions were within the acceptable limits. The validity criteria of the test guideline were met.

The OECD 211 test guideline is primarily designed to assess effects on Daphnia reproductive output (living young) as the primary population relevant endpoint. Measuring and reporting other biological parameters such as growth, %immobile young, time to first brood and %aborted eggs is optional. These biological parameters in addition to reproduction may assist in the overall interpretation of the study results; however, they alone are not indicative of a population relevant effect. A statistically significant difference in these additional parameters without an effect on reproduction is not considered in establishing the NOEC. No significant mortality or any other additional significant adverse effects or abnormal behavior were observed in any of the test treatments. The following overall effect concentrations (mg/L) are based on reproduction (living offspring per surviving adult) as the primary population relevant response and were obtained based on nominal concentrations:
LOEC = > 25 mg/L
NOEC = ≥ 25 mg/L
Since the measured concentrations of the test substance in the test solutions were within +20% of the nominal concentrations, the effect concentration can be expressed relative to the nominal concentration.

The purity of the test substance used in the test was 90.4%

LOEC = > 25 mg test substance/L or 22.6 mg a.i./L
NOEC = ≥ 25 mg test substance/L or 22.6 mg a.i./L

Key value for chemical safety assessment

Fresh water invertebrates

Fresh water invertebrates

Effect concentration:

22.6 mg/L

Additional information

Three reliable 21 d chronic toxicity studies for daphnids are available. A study from 2022 with EDTA-CuK2 which was performed in parallel to the study with the test substance (EDTA-ZnK2) and gave similar to the study with EDTA-CuK2 a 21d NOEC of 25 mg test substance/L.

There are also two older studies which both gave results in the same order of magnitude. The Key value used in the EU RAR 2004 is a study from BASF performed with EDTA-Na2H2 (CAS no 139-33-3). This study resulted similar as for EDTA-CuK2 and EDTA-ZnK2 in a 21d NOEC of 25 mg/L Recalculation towards EDTA-ZnK2 via MW ratio results in 431.8/336.21 x 25 = 32.1 mg/L