Phosphoric acid, mono- and di-C6-10-alkyl esters

PBT assessment

PBT assessment: overall result

PBT status:

the substance is not PBT / vPvB

Justification:

Persistence Assessment:

 

P criteria:

– the half-life in marine water is higher than 60 days, or

– the half-life in fresh- or estuarine water is higher than 40 days, or

– the half-life in marine sediment is higher than 180 days, or

– the half-life in fresh- or estuarine water sediment is higher than 120 days, or

– the half-life in soil is higher than 120 days

No experimental half-life data is available on the substance to compare against the persistence criteria, as a hydrolysis (abiotic degradation) study has not been conducted due to the following:

-         The test item is a complex reaction mixture with some components of very low water solubility. The test is not appropriate for complex reaction mixtures.

-         It was demonstrated in the assessment of the feasibility of the water solubility that it was not possible to obtain a true solution of the test item by either centrifugation or filtration.

Therefore, to asses the persistence of the substance, the results of the ready biodegradation study have been considered.

The biodegradation of the test item was assessed according to OECD Guideline 301B. The test item attained 115% degradation after 28 days and satisfied the 10-Day window validation criterion, whereby 60% degradation must be attained within 10 days of the degradation exceeding 10%. The test item can therefore be considered to be readily biodegradable under the strict terms and conditions of OECD Guideline No 301B.

Based on the screening criteria for P and vP, as the substance is readily biodegradable it does not meet the criteria for p or vP.

 

Bioaccumulation Assessment:

 

B criterion: BCF > 2000.

No experimental bioaccumulation study data is available on the substance and therefore no bioconcentration factor (BCF) is available to assess whether the substance meets the Bioaccumulation (B) criteria (BCF higher than 2000).

The experimental n-octanol.water partition coefficient (log₁₀Pow) result of Mean Log₁₀Pow: 3.15 to 4.51 and Mean Log₁₀Pow: >6.5, indicates that the majority of test substance and individual components have some potential for bioaccumulation. 

For the PBT and vPvB assessment a screening criterion has been established, which is log Kow greater than 4.5. The assumption behind this is that the uptake of an organic substance is driven by its hydrophobicity. For organic substances with a log Kow value below 4.5 it is assumed that the affinity for the lipids of an organism is insufficient to exceed the B criterion, i.e. a BCF value of 2000 L/kg (based on wet weight of the organism, which refers to fish in most cases).

 

Based on this screening criteria it can be proposed that the B critiera may be met based on the partition coefficient data. However, for some groups of chemicals, such as surface active compounds, log Kow is not always a valid descriptor for assessing the bioaccumulation potential. In addition, at very high log Kow (>6), a decreasing relationship between the two parameters (log BCF increasing linearly with log Kow ) is observed. Reduced uptake due to the increasing molecular size may play a role as well in potentially reducing BCF.

Therefore, in the absence of experimental bioaccumulation data, it can be considered that the B criteria may be met based on the log₁₀Pow data, but that this may be a worse case assessment.

 

Toxicity Assessment:

 

T critera:

– the long-term no-observed effect concentration (NOEC) for marine or freshwater organisms is

less than 0.01 mg/l, or

– the substance is classified as carcinogenic (category 1 or 2), mutagenic (category 1 or 2) or toxic

for reproduction (category 1, 2, or 3), or

– there is other evidence of chronic toxicity, as identified by the classifications: T, R48, or Xn, R48 according to Directive 67/548/EEC.

No long-term test results are available for marine or freshwater organisms and therefore no long-term NOEC results are available to compare against the toxicity criteria (NOEC less than 0.01 mg/l).

Algae was determined to be the most sensitive species based on the results of the acute studies in fish, Daphnia and algae and gave the following results from an algal inhibition study:

ErL₅₀(growth rate): >100 mg/l Loading Rate WAF, EyL₅₀(yield): 1.1 mg/l Loading Rate WAF, No Observed Effect Loading Rate: <1.0 mg/l.

 

Given that toxicity cannot be attributed to a single component (or a mixture of components) but to the test item as a whole the results were based on nominal loading rates only

Although this was a short-term algal test, it can be viewed as providing both acute and chronic endpoints, based on the short life cycle of Pseudokirchnerella subcapitata. The NOEC of <1.0 mg/l does not allow for conclusive assessment of whether the T criteria is met for a long-term NOEC of less than 0.01 mg/l.

 

No lethal or sub-lethal effects were observed in fish and the Daphnia magna study only showed minor effects at the top concentration tested (25% Daphnia immobile at nominal loading rate of 100 mg/l).It can be anticipated from these results that a long-term study in fish or Daphnia would not result in a NOEC of lower than 0.01 mg/l and further testing is considered to be unnecessary to asses the T criteria.

 

The substance is not currently classified as carcinogenic, mutagenic (category 1 or 2) or toxic for reproduction (category 1, 2 and 3)or classified as STOT RE (category 1 or 2) and there is no other evidence of chronic toxicity based on the available study data.

The substance is therefore not considered to meet the Toxicity (T) criteria.

Based on the data available, it is considered that the substance does not meet the criteria for persistence (P or vP) or toxicity (T-), but may potentially meet the criteria for bioaccumulation (B).

The substance is therefore not classed as a PBT or vPvB substance.