CONTRACT RESEARCH & TOXICOLOGY
Figure 4 – Conclusions of persistence assessment for HBCDD at each stage
Firstly , a scoring methodology was developed to assess the quality of individual studies . This evaluates studies according to both reliability and relevance to produce numerical scores for each , as well as an overall quality score .
Some fields have potential ‘ critical fails ’ where conditions have severe implications for study quality . In such cases , studies are automatically scored zero for either reliability and / or relevance . Numerical scores are rated qualitatively as low , medium or high . Difficult test substances have additional special rules during scoring , such as testing volatile substances in an open system .
Rules were then developed for combining each study with other studies from the same information category ( lines of evidence ( LoEs )) to reach conclusions for them . The LoEs included simulation tests for water , sediment and soil , screening tests , computational methods , monitoring data and other relevant data ( other WoE ).
The evaluation includes an assessment of the persistence outcome and the strength of the evidence for each LoE . Based on the study input and their quality scores , a representative half-life is produced for the simulation test data , temperature-corrected by default to 12 o C for soil and fresh or estuarine water and sediment , or 9 o C for marine water and sediment , in accordance with REACH guidance .
A scheme was developed for then combining individual LoEs to reach persistence assessment conclusions for a substance ( Figure 2 ). This takes account of the REACH persistence assessment guidance by prioritising the outcome of simulation tests , followed by ready biodegradability tests .
If a conclusive outcome cannot be reached from either of these tiers , a quantitative WoE ( qWoE ) methodology is applied , considering the outcome , strength and weighting of all LoEs together . Finally , a consistency check is conducted to assess extent of agreement across individual LoEs . In addition , POV can be calculated using the in-built multimedia fate model SimpleRisk4PAT , using the representative half-lives determined by PAT as inputs .
Case study results
The PAT has been tested with a case study substance , hexabromocyclododecane ( HBCDD : CAS 25637-99-4 ), a common brominated flame retardant . Numerous studies are available across several LoEs and these were input into PAT . The PAT assessed the quality of these studies and summarised the persistence indications of the individual study inputs across different lines of evidence ( Figure 3 ).
The first stage of the assessment considered the simulation tests for each environmental compartment . Both soil simulation tests were assigned high quality by the PAT . The half-lives of 134 and 238 days at 12 o C indicated HBCDD to be P and vP , respectively . Overall , the soil LoE was considered a moderate quality dataset and concluded that it was vP .
For freshwater sediment , the dataset consisted of three studies that spanned high , medium and low quality , and halflives of 23 days , ( not P ) to 214 days ( vP ), at 12 o C . The freshwater sediment LoE was overall of moderate quality ,
with a representative half-life of 214 days concluding vP .
The second stage considered the RBT data available . The only RBT for HBCDD was scored as high quality and , as no degradation was observed , it was concluded to be potentially P .
Considering all the available evidence together as part of a qWoE determination in stage three , HBCDD was indicated as P / vP ( stage three does not distinguish between the two ). This step additionally considers indications from computational predictions , monitoring data and other evidence that was not able to be input into any of the specific LoE categories .
Finally , the overall conclusion of the persistence assessment within the PAT is that HBCDD is vP . There was overall consistency across all lines of evidence in reaching this conclusion .
Outlook
The development of the PAT leverages the long-established experience of Ricardo , Concawe , ICCS , CEFIC and ECETOC to advance thinking , practice , concepts and frameworks so that persistence assessment methodology is fit for purpose in the 21st century .
The PAT is specifically intended to improve consistency , transparency and robustness in persistence assessments . Coming at a time of extensive change in regulatory guidance and policy areas , the tool has the potential for a significant impact in both . ●
Chris Hughes
RICARDO k + 44 1234 987654 J enquiry-ee @ ricardo . com j www . ricardo . com / pat
24 SPECIALITY CHEMICALS MAGAZINE ESTABLISHED 1981