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PBT assessment

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PBT assessment: overall result

PBT status:
the substance is not PBT / vPvB

The substance exhibited ready biodegradability in a CO2 evolution test conducted on an analogue substance through read-across (i.e., 69% degradation in 29 days, not meeting the 10-d window); the 10-day window does not apply to multi-constituent and UVCB substances and the test material (as a UVCB) may thus be considered readily biodegradable. In addition, a validated QSAR model (EPI Suite BIOWIN 4.10) predicted that the substance itself is readily biodegradable, based on two modules within the model: BIOWIN 3, which predicted ultimate degradation of the substance in the timeframe of “weeks”, and BIOWIN 5, which predicted that the substance “biodegrades fast”.  Four additional modules within the model (BIOWIN 1, BIOWIN 2, BIOWIN 6 and BIOWIN 7) predicted that the substance “biodegrades fast”; one module (BIOWIN 4) predicted that primary degradation occurs within the timeframe of “days”.  In summary, the QSAR prediction indicates that the substance does not contain any structural components that are refractory to rapid environmental degradation; this prediction is verified by the laboratory test on the analogue substance.  Therefore, although a definitive determination has not been made, the substance is considered “not P” and “not vP” based upon the screening criteria and multiple lines of evidence.   

Aquatic bioaccumulation testing was not conducted on the substance, and therefore the bioaccumulative properties of the substance cannot be definitively determined. One screening-level datum indicates that the substance may be potentially bioaccumulative (potentially B) and potentially very bioaccumulative (potentially vB), i.e., the predicted octanol-water partition coefficient (log Kow) of 6.30, which is above the screening criterion (log Kow≤ 4.5) for both “not B” and “not vB”.  However, this estimated value is a “very high” value (i.e., log Kow > 6).  For substances with a very high partition coefficient, a decreasing relationship between log Kow and bioconcentration factor (BCF) is observed.  Therefore, the octanol-water partition coefficient for the substance may not be an effective predictor of its actual bioaccumulation potential.  Additionally, available information indicates that the substance exhibits a low potential for aquatic exposure, based on its very low water solubility (estimated at 0.01038 mg/L) and strong adsorption to soils, sediment and activated sludge (estimated log Koc = 3.98).   Additional information indicates that the substance exhibits a low potential for bioaccumulation. The substance is composed of a polyhydroxylated alkyl ester of a fatty acid, and is expected to be rapidly metabolised in vertebrates, indicating that the potential for bioaccumulation may be much lower than that predicted by the partition coefficient. The bioconcentration factor (BCF = 281 L/kg w.w.) predicted by a validated QSAR model (EPI Suite BCFBAF v3.01) is substantially below the criteria for both bioaccumulative (BCF > 2000) and very bioaccumulative (BCF > 5000).  Therefore, although a definitive determination has not been made, the substance is considered “presumably not B” and “presumably not vB”, based upon multiple lines of evidence (including toxicokinetics and QSAR modeling).     

The evaluation of short-term aquatic toxicity tests indicates that the substance exhibits a low potential for both acute and chronic aquatic toxicity. Toxicity studies (conducted on analogue substances through read-across) reported acute toxicity values of 96-h LLR50 > 100 mg/L and 72-h ErLR50 > 100 mg/L from acute fish toxicity and algal growth inhibition studies, respectively. These results indicate that the short-term toxicity levels of the substance are substantially above the screening criterion for potential aquatic toxicity (EC50 or LC50 < 0.1 mg/L).  Similarly, toxicity studies conducted on the same analogue substances reported long-term toxicity values of 21-d NOELR ≥ 1.0 mg/L and 72-h NOErLR = 11 mg/L in a chronic daphnid reproduction test and algal growth inhibition study, respectively. These results indicate that the long-term toxicity levels are substantially above the criterion (NOEC < 0.1 mg/L) below which a substance may be definitively determined to be toxic to aquatic organisms. The substance does not exhibit the properties of a carcinogenic, mutagenic or reproductive toxicant (CMR), nor does the substance exhibit specific target organ toxicity in a repeated-dose study (STOT-RE). These results provide a definitive determination that the substance is not toxic with respect to mammalian endpoints. Thus, it has been shown by both definitive criteria (mammalian toxicity and long-term aquatic toxicity) and by screening criteria (short-term aquatic toxicity) that the substance is “not T”.     

Therefore, although a complete definitive determination cannot be made with respect to all endpoints, it has been shown by definitive criteria that the substance is “not T” (mammalian toxicity and long-term aquatic toxicity); by screening criteria that that the substance is “not P”, “not vP” and “not T” (based on short-term aquatic toxicity); and by multiple lines of evidence that the substance is “presumably not B” and “presumably not vB”.  It is not necessary to have definitive criteria for all five endpoints to make the determinations as to whether the substance is “not PBT” and “not vPvB”. The determination only requires that “each of the three properties persistency, bioaccumulation and toxicity need to be considered in conjunction” (Chapter R.11, “PBT Assessment”, Guidance on information requirements and chemical safety assessment, Version 1.1, ECHA, November 2012, Section R., p. 15).    In summary, based on data available to date, the substance is “not PBT” (not P, presumably not B, and not T based on aquatic and mammalian endpoints) and is “not vPvB” (not vP, presumably not vB).