2-mercaptoethanol

Ecotoxicological Summary

Hazard for aquatic organisms

Freshwater

Hazard assessment conclusion:

PNEC aqua (freshwater)

PNEC value:

0.006 mg/L

Assessment factor:

10

Extrapolation method:

assessment factor

PNEC freshwater (intermittent releases):

0.004 mg/L

Marine water

Hazard assessment conclusion:

PNEC aqua (marine water)

PNEC value:

0.001 mg/L

Assessment factor:

100

Extrapolation method:

assessment factor

STP

Hazard assessment conclusion:

PNEC STP

PNEC value:

60 mg/L

Assessment factor:

1

Extrapolation method:

assessment factor

Sediment (freshwater)

Hazard assessment conclusion:

PNEC sediment (freshwater)

PNEC value:

0.024 mg/kg sediment dw

Extrapolation method:

equilibrium partitioning method

Sediment (marine water)

Hazard assessment conclusion:

PNEC sediment (marine water)

PNEC value:

0.002 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:

PNEC soil

PNEC value:

0.908 mg/kg soil dw

Extrapolation method:

assessment factor

Hazard for predators

Secondary poisoning

Hazard assessment conclusion:

no potential for bioaccumulation

Conclusion on classification

Acute tests on all three trophic levels were performed to examine the aquatic toxicity of 2 -mercaptoethanol. Daphnia magna turned out to be the most sensitive species revealing an EC50 (48 h) of 0.4 mg/L. Thus, 2-mercaptoethanol is considered acutely very toxic for aquatic organisms (Acute Aquatic Toxicity Category 1: H400), with an M factor of 1.

Chronic toxicity data are available for 2-mercaptoethanol for algae and Daphnia, and Daphnia magna turned out to be the most sensitive species with a NOEC of 0.0632 mg/L. The available chronic data would meet the criteria for chronic category 1 for non-rapidly degradable substances and chronic category 2 for rapidly degradable substances.

A surface water mineralisation study (Brands 2016) indicates that 2-mercaptoethanol would have a half-life of 0.079 days and so would be removed from the aquatic environment to a level of >70% within a 28-day period. Mineralisation was a significant route of degradation and activity recovered as CO2 increased to more than 60% after 14 days of incubation at both test concentrations. Three major transformation products were detected which exceeded 10% of applied activity at both test concentrations. Transformation product M-1 reached a maximum of 26% after 4 hours (0.17 days) at the low test concentration and a maximum of 13% after 8 hours (0.33 days) at the high test concentration, and then decreased to non-detectable amounts after 6 days of incubation (both concentrations). Transformation product M-3 reached a maximum of 36% (low test concentration) and 30% (high test concentration) after 2 days and then decreased to 14% after 9 days of incubation (low test concentration) and to <5% after 14 days of incubation (high test concentration). Transformation product M-6C reached a maximum of 41% (low test concentration) and 39% (high test concentration) after 4 hours (0.17 days) and then decreased to non-detectable amounts after 6 days of incubation. This indicates that 2-mercaptoethanol and its transformation products would be removed from the aquatic environment to a level of >70% within a 28-day period and therefore is considered rapidly degradable.

On the basis of the available data, 2-mercaptoethanol is considered to meet the criteria for classification as very toxic to aquatic life (Acute Aquatic Toxicity Category 1: H400, M factor: 1) and toxic to aquatic life with long lasting effects (Chronic Aquatic Toxicity Category 2: H411).