D-gluconic acid, compound with N,N''-bis(4-chlorophenyl)-3,12-diimino-2,4,11,13-tetraazatetradecanediamidine (2:1)

Sediment toxicity

Description of key information

The influence of Chlorhexidin Digluconate Solution 20 % on emergence of midges of the freshwater dipteran Chironomus riparius was investigated following the OECD guideline 218. The sediment-dwelling larvae (first instar) were placed in a sediment-water test system with defined artificial sediment. The sediment was spiked with the test item at nominal concentrations of 0.644, 1.288, 2.575, 5.15, 10.3 and 20.6 mg a.i./kg sediment (dwt). The effect values were based on measured test substance concentrations in the stock solution. In this study, although small deviations of water temperature variation and time of emergence from the recommend-ed values of the guideline occured, the primary validity criterion (hatching rate > 70 % at test end; even achieved after day 23), paraphrased by the verb “must” was fulfilled. In the test guideline, the validity criteria time of hatch and temperature are para-phrased with the verb “should” and thus indicate minor deviations are tolerable. The small deviations of water temperature, and emergence time are considered to have no impact on the quality and integrity of the study. As a result, an effect on emergence rate and development time or rate was detected when compared to the control midges. The effects showed a clear concentration/effect dependency. The NOECs were found to be 4.33 mg a.i./kg dwt for the emergence rate and 15.0 mg a.i./kg dw for the development rate. There were no indications for a different sensitivity of sexes.

In a second study, the effects on biomass, weight, survival rate and reproduction rate of the amphipod Hyalella azteca was investigated following the test principles by US EPA ringtest, Environment Canada, and ASTM. A 42 day static exposure to Chlorhexidin di-gluconat 20 % aqueous solution at different concentrations with a single application of the test item at test start was conducted. Untreated control replicates were run in parallel. To ensure a sufficient reproduction rate, the Hyalellas in this study additionally were fed with phytoplankton (diatoms Thalassiosira weissflogii 1200TM® by ReedMariculture Inc.) and TetraMin® during the test. The amount of phytoplankton and TetraMin® was enhanced during the test. The kind of food and feeding regime followed the US EPA ringtest and therefore also the recommendation of the current DRAFT revision US EPA Sediment Toxicity and Bioaccumulation Meth-ods. Renewal of the overlying water was not conducted. However, the oxygen demand from sediment was overcome and adequate water quality in the overlying water maintained, so that renewal was not necessary. In contrast, this has secured the degree of ex-posure without affected amphipods. In the study 6-7 d old amphipods have been used at test start. This is slightly lower than the recommended 7-8 d old amphipods. Even when reproduction occurring in the sediment exposure phase had not to be avoided in the current study, the guideline wording shows that not the age of the specimens introduced, but the growth and reproduction conditions are relevant. In this study, improved diet was applied and growth and reproduction rate surpassed the validity criteria. In some replicates 11 adults were found at test end, instead of 10. For evaluation of weight on replicate basis, replicates with more than 10 specimens introduced were neglected from evaluation. The approach applied is nearly totally in accordance with the current DRAFT revi-sion US EPA Sediment Toxicity and Bioaccumulation Methods. Neglecting 1 – 2 replicates with 11 adults out of eight replicates per treatment level is expected to have no effect on the integrity of the results and their evaluation. Beside this, the most sensitive end-point reproduction was evaluated using eight replicates per treatment level. This deviation is considered to have no influence on the test result. Each treatment group consisted of 8 replicates with ten amphipods each (12 replicates in total are necessary to deter-mine 28-day mortality. However, mortality after 28 d is not mandatory, and thus 8 replicates are sufficient for 42 day reproductive endpoints). The sediment was spiked with the test item at nominal concentrations of 60.4, 121, 242, 484, and 967 mg a.i./kg sedi-ment (dwt). The application solutions for all treatment levels were verified analytically and found to be 96.0 – 103.0 % of nominal. The effect values were based on nominal test substance concentrations due to extremely low recovery rates. No effect on survival, biomass and reproduction rate was detected when compared to the control Hyalella. The relevant NOEC is ≥967 mg a.i./kg dw. Ac-cording to current US EPA Sediment Toxicity and Bioaccumulation Methods “Average survival of H. azteca in the control sediment on Day 28 should be greater than or equal to 80%.”. In addition, further acceptability criteria are given in the current DRAFT revision US EPA Sediment Toxicity and Bioaccumulation Methods. All validity criteria for day 42 were surpassed. The results and evaluation and interpretation of the study are plausible, and suitable to be applied in a risk assemsment for sediment dwellers. Overall, the study is in accordance to the design applied in a US EPA ringtest and a new test design proposal of Environment Canada, where continous sediment exposure through the reproductive phase is applied, with young recovered directly from the sediment. This approach is already referred in the US EPA Sediment Toxicity and Bioaccumulation Methods DRAFT revision. The test results revealed are valid according to current and draft guidelines.

In the third study, the effects on development (mortality, reproduction rate and biomass) of the endobenthic oligochaete Lumbricu-lus variegatus was investigated following the OECD guideline 225. Worms of similar physiological state were placed in a sediment-water test system with defined artificial sediment. The sediment was spiked with the test item at nominal concentrations of 60.4, 121, 242, 484, and 967 mg a.i./kg sediment (dwt). The application solutions for all treatment levels were verified analytically and found to be 94.9 – 119.2 % of nominal. The effect values were based on nominal test substance concentrations due to extremely low recovery rates. An effect on total number of living worms was detected when compared to the control worms. The NOECs were found to be 484 mg a.i./kg dwt for total number of living worms and ≥967 mg a.i./kg dw for weight and biomass.

Key value for chemical safety assessment

EC10, LC10 or NOEC for freshwater sediment:

4.33 mg/kg sediment dw

Additional information

Lowest NOEC from three chronic reliable GLP sediment studies.