Inorganic residual from kraft or soda pulping separated from green liquor in the chemical recovery cycle.

Endpoint summary

Key value for chemical safety assessment

Acute toxicity: via oral route

Endpoint conclusion

Dose descriptor:

discriminating dose

Value:

5 000 mg/kg bw

Acute toxicity: via dermal route

Endpoint conclusion

Dose descriptor:

discriminating dose

Value:

2 000 mg/kg bw

Additional information

Green liquor sludge contains several alkaline metal compounds/salts such as hydroxides, oxidised sulfur constituents (sulfates, thiosulfate and sulfites) and carbonates. Acute toxicity values for all of these compounds have been earlier characterized extensively in animal studies and reviewed in CSR report to Green liquor sludge. A lot of human data for these substances can be also found, because these compounds have been in the industrial use during decades. From the GLS compounds carbonates and hydroxides are rapidly dissolved and resulted nontoxic metabolites, which are removed from the body mainly via kidneys. Because of their rapid inactivation, these compounds are not believed to result in systemic toxicity and they have relatively low acute toxicity levels according the earlier animal experiments. However, due to their alkaline properties an irritation and corrosiveness to skin, respiratory tract and trachea is noticed depending on their concentrations. 

Acute inhalation toxicity for sulfides and oxidised sulfur constituents seem to be very low when pH is maintained on alkaline side. However, hydrogen sulfide gases (H₂S) are toxic, lethal if inhaled in high concentrations. H₂S may evaporated from GLS in contact with acids. If H₂S gas is evolved it will be the most toxic compound in GLS and lethal concentrations in animal experiments are: LC50 335 ppm 6 hours for rats and LC100 722 ppm 50 minutes for mice. The lowest lethal dose evaluated for humans in accidental case reports was only 76 ppm of hydrogen sulfide. However, no sulfides were detected in the GLS samples determined in the studies for this report.The pH of GLS is over 12 and it is unlikely that hydrogen sulfide is released in gaseous form under normal handling conditions.

Acute oral and dermal toxicity experiments with rats verified low acute toxicity values for GLS. The LD_50,oralwas determined to be > 2000 mg/kg body weight. Based on the guidance given in OECD guideline 423 (annex 2c), the LD_50,oral can be assessed to be > 5000 mg/kg body weight. According to the decision trees of the OECD Guideline and the EC Directive the LD_50,dermal of GLS is higher than 2000 mg/kg body weight in rats.

 

No test results are available for inhalation route. GLS is a non volatile solid substance. However, it may form inhalable dusts like any other solid powders when dry. Particle size distribution study indicate (468 µm (50%), 9 µm (10 percentile)) that only a small fraction might enter the small alveoli. The acute inhalation of GLS dust may cause discomfort and stress as well as sign of local irritation to nasal, bronchiolar and ocular mucous membranes. Highly alkaline mists are acutely toxic if inhaled. However, GLS is a solid paste that contains >50% water before drying and therefore it is unlikely that alkaline mists can be formed. The alkality is also rapidly reduced by the influence of CO₂ in the air. We can hypothesize that GLS's acute inhalation toxicity caused by OH- ions reduces rapidly with time and distance. Acute inhalation toxicity for sulfides and oxidised sulfur constituent seem to be very low when pH is maintained in alkaline side. In conclusion, GLS dusts are expected to be acutely non-toxic via inhalation route.

 

Justification for classification or non-classification

Acute oral and dermal toxicity experiments with rats verified low acute toxicity for Green liquor sludge.

The LD_50,oral was > 2000 mg/kg (wet wt. test material) body weight in rats.

The LD_50,dermal was > 2000 mg/kg (wet wt. test material) body weight in rats.

Acute toxicity for inhalation route is expected to be low, based on route-to-route extrapolation from the oral and dermal test results.

As a conclusion, the acute systemic toxicity for the tested patch of GLS is very low and overall classification for acute toxicity for GLS is not needed.

Classification for Acute toxicity:

No classification