Xylitol

Ecotoxicological Summary

Hazard for aquatic organisms

Freshwater

Hazard assessment conclusion:

PNEC aqua (freshwater)

PNEC value:

75.5 mg/L

Assessment factor:

1 000

PNEC freshwater (intermittent releases):

755 mg/L

Marine water

Hazard assessment conclusion:

PNEC aqua (marine water)

PNEC value:

7.5 mg/L

Assessment factor:

10 000

STP

Hazard assessment conclusion:

no hazard identified

Sediment (freshwater)

Hazard assessment conclusion:

PNEC sediment (freshwater)

PNEC value:

270 mg/kg sediment dw

Extrapolation method:

equilibrium partitioning method

Sediment (marine water)

Hazard assessment conclusion:

PNEC sediment (marine water)

PNEC value:

14.7 mg/kg sediment dw

Extrapolation method:

equilibrium partitioning method

Hazard for air

Air

Hazard assessment conclusion:

no hazard identified

Hazard for terrestrial organisms

Soil

Hazard assessment conclusion:

no hazard identified

Hazard for predators

Secondary poisoning

Hazard assessment conclusion:

no potential for bioaccumulation

Additional information

The modes of toxic action in ecotoxicology have been studied to a great extent and as a result, there are many (Q)SARs for aquatic toxicity endpoints available. Verhaar et al (1992) associated four modes of action with structural characteristics which provided a convenient means of categorising substances. The four modes of action were respectively: inert, less inert, reactive and specifically acting chemicals. The first ‘inert’ is otherwise termed ‘narcotic’ or ‘neutral organic’ in order to indicate a narcosis mode of action. Hydrophobicity has been found to be a key chemical feature in determining the effects of narcotic organic compounds in aquatic systems (Donkin, 1994). The most common measure of hydrophobicity is LogKow. Konemann (1981) developed the ‘classic’ general narcosis (Q)SAR for toxicity to Poecilia reticulata (guppy) which related LogKow to LC50 (Log of the molar LC50). This was subsequently found to be applicable for prediction of toxicity to a range of aquatic species, not only other fish species but other organisms such as Daphnia magna. ECOSAR v1.11 for example contains a variant on this general narcosis equation for fish, Daphnia and green algae.

 

Xylitol is expected to act as a neutral organic chemical based on chemical inspection. Within the OECD Toolbox v3, the Verhaar MOA, the OASIS MOA for Aquatic Toxicity and ECOSAR all categorised Xylitol as a neutral organic. Thus, the aquatic toxicity as expressed as a molar Log of the LC50 or EC50 could be predicted using LogKow. Xylitol also does not contain any functional groups that would be indicative of electrophilic potential i.e. it does not trigger any alerts for protein binding or DNA binding as encoded in the OECD Toolbox which substantiates the expectation that Xylitol will act as a neutral organic.

 

Donkin, P., 1994. Quantitative structure-activity relationships. In: Calow, P. (Ed.), Handbook of Ecotoxicology, vol. 2. Blackwell Scientific Publications, London.

Konemann, H., 1981. Quantitative structure-activity relationships in fish toxicity studies 1. Relationship for 50 industrial pollutants. Toxicology 19, 209–221.

Verhaar HJM, van Leeuwen CJ, Hermens JLM (1992).Classifying environmental pollutants. 1. Structure-activity relationships for prediction of aquatic toxicity. Chemosphere 25, 471-491.

Conclusion on classification

A QSAR approach based on the baseline narcosis equation using LogKow as an input variable exploiting the functionality encoded in ECOSAR was undertaken to derive information to characterise the aquatic toxicity to fish, daphnia and algae species. Xylitol was found to be of low concern to all 3 aquatic species. Screening studies available in Ceriodaphnia dubia and Pimephales promelas substantiate the predicted low toxicity of the substance. Therefore, the test substance is not classified for acute or chronic aquatic toxicity according to EU Classification, Labelling and Packaging of Substances and Mixtures (CLP) Regulation (EC) No. 1272/2008.