Sulphur trioxide

Additional ecotoxological information

Administrative data

Endpoint:

additional ecotoxicological information

Type of information:

experimental study

Adequacy of study:

supporting study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

study well documented, meets generally accepted scientific principles, acceptable for assessment

Remarks:

Published, investigative non-guideline, non-GLP study.

Cross-reference

Cross-reference 1

Reason / purpose for cross-reference:

reference to same study

Cross-reference 2

Reason / purpose for cross-reference:

read-across source

Reference

Endpoint:

additional ecotoxicological information

Type of information:

read-across from supporting substance (structural analogue or surrogate)

Adequacy of study:

supporting study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

study well documented, meets generally accepted scientific principles, acceptable for assessment

Remarks:

Published, investigative non-guideline, non-GLP study.

Justification for type of information:

Sulphur trioxide readily reacts with water to form sulphuric acid. The reaction is instantaneous, to the extent that SO3 will react with water vapour in the atmosphere to form fumes of sulphuric acid. This reaction forms the basis of the manufacturing process of H2SO4. The read-across hypothesis is therefore that SO3 will instantaneously transform into H2SO4 upon contact with water (i.e. in aquatic ecotoxicology tests), thus any observed effects will be directly attributable to sulphuric acid. It is therefore justifiable to derive hazard conclusions from sulphuric acid data, with regard to ecotoxicological endpoints.

Reason / purpose for cross-reference:

reference to same study

Reason / purpose for cross-reference:

read-across source

Qualifier:

no guideline available

Principles of method if other than guideline:

The pH of Lake 223, Ontario, Canada, was lowered from 6.7 in 1974 to 5.1 by 1981. Samples of cladocera were taken each year and the species composition and overall biomass were monitored.

GLP compliance:

no

Type of study / information:

Published paper describing experimentally derived results.

Specific details on test material used for the study:

Available study data for sulphuric acid is being used for read-across to the target substance, sulphur trioxide.

Total zooplankton biomass was not reduced by acidification and may have increased in 1980. Prior to acidification, mean ice-free season biomass was 269 mg/m2, during 1977 to 1980 it was 318, 218, 204 and 401 mg/m2 respectively. During 1981 to 1984 biomass was 279, 236 and 247 mg/m2. Although total biomass did not greatly change with acidification, total biomass of cladocerans increased during1918 to 1983. This occurred at the expense of calanoid copepods and to a lesser extent cyclopoid copepods. In 1974 adults of D. minutus were present at a biomass of 33 mg/m2. During 1981 to 1983 their biomass was 26, 17 and 24 mg/m2. Cladocerans also exhibited marked changes in species composition. The community in 1974 at pH 6.7 was dominated by Daphnia galeata mendotae with Diaphanosoma birgeiand Bosmina longirostris also present, Holopedium gibberum was rare. At pH 5.1 Daphnia catawba, H. gibberum and B. longirostris were all abundant. D. birgei and D. g. mendotaehad dissappeared or become rare. D. catawba recorded for the first time in 1980 was usually the sole daphnid at pH 5.1, it replaced D. g.mendotaealmost entirely during the 1918 to 1983 period. Chaoborus has been incidentally samples along with the zooplankton, there is no evidence it changed markedly in abundance with acidification.

Conclusions:

The reported study is adequate in demonstrating the effects of lowering pH on the compostion and structure on cladocera.

Executive summary:

Data on the toxicity to zooplankton is available for sulphuric acid and is considered suitable for read-across (based on the analogue approach) to the target substance, sulphur trioxide. Sulphur trioxide readily reacts with water to form sulphuric acid. The reaction is instantaneous, to the extent that SO₃ will react with water vapour in the atmosphere to form fumes of sulphuric acid. This reaction forms the basis of the manufacturing process of H₂SO₄. The read-across hypothesis is therefore that SO₃ will instantaneously transform into H₂SO₄ upon contact with water (i.e. in aquatic ecotoxicology tests), thus any observed effects will be directly attributable to sulphuric acid. It is therefore justifiable to derive hazard conclusions from sulphuric acid data, with regard to ecotoxicological endpoints.

The zooplankton community was analysed by identifying the species and counting them. A NOEC for population repartition (from copepod to cladoceran dominance) was pH 5.59 (equivalent to 0.13 mg/L). This NOEC integrates not only reproductive success, but also prey/predator relationships, (presence/lack of suitable food as smaller invertebrates or aquatic plants/algae, presence/lack of fish predators). The NOEC also integrates the effects of successive one-tear exposures to pH 6.49, 6.13, 5.93 and 5.64.

Data source

Reference

Reference 1

Reference Type:

publication

Title:

Increase in the abundance of cladocera at pH 5.1 in experimentally-acidified Lake 223, Experimental Lakes Area, Ontario

Author:

Malley, DF & Chang, PSS

Year:

1986

Bibliographic source:

Water, Air, and Soil Pollution 30 (1986) 629-638

Reference 2

Reference Type:

secondary source

Title:

SULFURIC ACID CAS No. 7664-93-9: SIDS Initial Assessment Report for 11th SIAM

Author:

OECD

Year:

2001

Bibliographic source:

UNEP Publications

Materials and methods

Test guideline

Qualifier:

no guideline available

Principles of method if other than guideline:

The pH of Lake 223, Ontario, Canada, was lowered from 6.7 in 1974 to 5.1 by 1981. Samples of cladocera were taken each year and the species composition and overall biomass were monitored.

GLP compliance:

no

Type of study / information:

Published paper describing experimentally derived results.

Test material

Test material information

Constituent 1

Reference substance name:

Sulphuric acid

EC Number:

231-639-5

EC Name:

Sulphuric acid

Cas Number:

7664-93-9

Molecular formula:

H2O4S

IUPAC Name:

sulfuric acid

Details on test material:

None available

Results and discussion

Any other information on results incl. tables

Total zooplankton biomass was not reduced by acidification and may have increased in 1980. Prior to acidification, mean ice-free season biomass was 269 mg/m2, during 1977 to 1980 it was 318, 218, 204 and 401 mg/m2 respectively. During 1981 to 1984 biomass was 279, 236 and 247 mg/m2. Although total biomass did not greatly change with acidification, total biomass of cladocerans increased during1918 to 1983. This occurred at the expense of calanoid copepods and to a lesser extent cyclopoid copepods. In 1974 adults of D. minutus were present at a biomass of 33 mg/m2. During 1981 to 1983 their biomass was 26, 17 and 24 mg/m2. Cladocerans also exhibited marked changes in species composition. The community in 1974 at pH 6.7 was dominated by Daphnia galeata mendotae with Diaphanosoma birgeiand Bosmina longirostris also present, Holopedium gibberum was rare. At pH 5.1 Daphnia catawba, H. gibberum and B. longirostris were all abundant. D. birgei and D. g. mendotaehad dissappeared or become rare. D. catawba recorded for the first time in 1980 was usually the sole daphnid at pH 5.1, it replaced D. g.mendotaealmost entirely during the 1918 to 1983 period. Chaoborus has been incidentally samples along with the zooplankton, there is no evidence it changed markedly in abundance with acidification.

Applicant's summary and conclusion

Conclusions:

The reported study is adequate in demonstrating the effects of lowering pH on the compostion and structure on cladocera.

Executive summary:

The zooplankton community was analysed by identifying the species and counting them. A NOEC for population repartition (from copepod to cladoceran dominance) was pH 5.59 (equivalent to 0.13 mg/L). This NOEC integrates not only reproductive success, but also prey/predator relationships, (presence/lack of suitable food as smaller invertebrates or aquatic plants/algae, presence/lack of fish predators). The NOEC also integrates the effects of successive one-tear exposures to pH 6.49, 6.13, 5.93 and 5.64.