Reaction products of sodium glucoheptonate with zinc sulfate and sodium hydroxide

Endpoint summary

Description of key information

Fish

The regarded studies indicate that the LC50-values of ZnGHA on fish are clearly above the cut-off value for classification of 1 mg/L. In addition, it was shown, that water hardness significantly decreases zinc toxicity (Lloyd, 1961, Sinley et al., 1974), whereas a decrease of pH does not show a clear effect, as demonstrated for other species (Schubauer-Berigan et al., 1993). Regarding life-stage, eyed eggs of O. mykiss were found to be one of the more resistant stages in the life cycle (Sinley et al., 1974). In the case of O. tschawytscha, newly hatched alevins were much more tolerant to zinc than were later juvenile forms. However, the later progression from swim-up alevin, through parr, to smolt was accompanied by a slight increase in metal tolerance (Chapman, 1978).

The LC50 (30 d)-values for O. mykiss converted to ZnGHA range between 2.13 and 12.43 mg ZnGHA/L; the NOEC (30 d) lies between 1.26 and 4.87 mg/L. This difference is caused by the protective impact of increased Ca and DOC concentration (De Schamphelaere et al., 2005). In addition, water hardness was found to reduce zinc toxicity (Sinley et al., 1974). Besides, it was shown, that fish not exposed to zinc as eggs may be as much as four times more susceptible to zinc than fish exposed to zinc as eggs (Sinley et al. 1974).

Invertebrates

In the key study an EC50 (48 h) value of 24.9 mg ZnGHA/L was obtained for Daphnia magna (Kamle, 2017).When comparing to EC50 (48 h)-values for D. magna found in literature and converted to the target substance ZnGHA, the value obtained in the key study exceeds the other values (table 1). There are several studies underlining the fact, that aquatic zinc toxicity significantly depends on environmental factors like pH-value (Schubauer-Berigan et al. 1993, Hyne et al. 2005), water hardness (Hyne et al. 2005,Barata et al. 1998) and dissolved organic carbon (DOC) content (De Schamphelaere et al. 2005).

The chronic EC50(21 d)-values for D. magna range between 0.71 mg ZnGHA/L and 3.38 mg ZnGHA/L and the NOEC lies between 0.4 and 3.1 mg ZnGHA/L (De Schamphelaere et al., 2005). This variation is explained by the protective effect of Na and DOC. Both concentrations are higher in the sample with the lower EC. In addition, the pH is decreased. pH has been shown to reduce zinc toxicity to D. magna, significantly (De Schamphelaere et al., 2005). The EC50-values obtained by Muyssen and Janssen (2002), converted to ZnGHA range between 2.23 and 3.09 mg ZnGHA/L. The chronic test results indicate that organisms acclimated to 50 and 100 µg Zn/L performed better (survival and reproduction), than organisms acclimated to lower concentrations of Zinc (3 and 13 µg Zn/L).

Algae

It was shown, that several environmental factors impact the toxicity of zinc to algae leading to a great variation in the EC-values. In general, algae are very sensitive to zinc. When converting the EC50-values found for elemental zinc in literature to ZnGHA, all values, except for measurements at pH <7 and the value for Chlorella sp. at pH 7, are below 1.5 mg ZnGHA/L. The lowest ErC50 value of the regarded studies is between 0.25 – 0.38 mg ZnGHA/L for Nitzschia closterium (Fisher and Frood 1980) (table 1). The highest values for ZnGHA are found at pH 5.5 with 12.94 mg ZnGHA/L for P. subcapitata (De Schamphelaere et al. 2005) and at pH 5.7 with 17.04 mg ZnGHA/L for Chlorella sp. (Wilde 2006). Thus, the value of 0.89 mg ZnGHA/L derived in the key study at neutral pH (Kamle, 2017) lies within the range of the values found in publications. Based on this value the substance would need to be classified as hazardous to the aquatic environment, acute category 1. However, there is evidence that the toxicity of zinc strongly depends on the chemical properties of the water like dissolved organic carbon (DOC) content (De Schampelaere et al. 2005, Fisher and Frood 1980), pH-value (Wilde et al., 2006, De Schamphelaere 2005), salinity (Eklund, 2005), metal concentration (De Schamphelaere et al. 2005). These factors are not accounted for in the standardised laboratory studys.

Microorganisms

The EC50-values for ZnGHA on microorganisms range between 2.21 and 504.95 mg ZnGHA/L. The maximum, as well as the minimum value were derived using activated sludge. This shows that there is a great variation between the different methods.