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Ecotoxicological information

Toxicity to terrestrial plants

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Description of key information

Based on the available terrestrial plant read-across “analogue” data (ExxonMobil Biomed Sciences Lab., 2009b) and the recent follow-up definitive dose-response study in radish (ExxonMobil Biomed Sciences Lab., 2013) , the registered substance would not be expected to have any adverse effect on seedling emergence or growth in plants.  The recent follow-up findings in radish clearly demonstrated no adverse effects or dose-response effects on growth and provided a 14-day NOEC >935 mg/kg (measured) for both emergence and growth.  Read-across data established a 14-day NOEC > 943 mg/kg in wheat and a 14-day NOEC > 962 mg/kg in mung bean plants for both emergence and growth for the registered substance.  Collectively, the follow-up radish and the read-across short-term terrestrial plant studies indicated registered substance would not be expected to cause any acute toxicity to terrestrial plants in terms of seedling emergence or growth.  No dose response in these endpoints was observed in radish from the lowest 100 mg/kg nominal to the highest 1000 mg/kg nominal soil exposure groups.    We will use nominal NOEC or EC50 values of > 1000 mg/kg soil in key value for short term EC50 since entry of data does not allow for including a range of values or greater than values. 
Based on a weight of evidence (WoE) assessment as discussed in Section 7.2.1.2 of the CSR and in the full WoE attachment in Section 13 of IUCLID, the registered substance is not expected to cause long-term toxicity. Using the EqPM-TLM framework model, the registered substance is not expected to cause long-term adverse effects in plants, owing to its high log Kow and low water solubility. It was not possible to determine a chronic NOEC value for the registered substance.

Key value for chemical safety assessment

Short-term EC50 or LC50 for terrestrial plants:
1 000 mg/kg soil dw

Additional information

Background summary of short-term terrestrial plant toxicity data:

Previously, limited data reported in three plant species (i.e., wheat, mung bean and radish) for the read-across “analogue” 1-decene dimer hydrogenated (CAS 68649-11-6)(a component of the registered substance) were used to assess the potential effect of the registered substance on seedling emergence and growth. Based on the analogue read-across data, the registered substance would not be expected to have any adverse short-term effects on seedling emergence in the above three plant species. In wheat and mung bean, the registered substance would not be expected to cause any short-term adverse effects on seedling growth. There were read-across data indicating a growth reduction (35% relative to controls) in radish which the Registrant expressed some concerns about since the growth effects might to due to possible physical effects (e.g. occlusive effect of oily material in soil on seedling, thus affecting water, oxygen or nutrition uptake mechanisms). 

 

As a technical concern, the growth effects reported in radish were indicated by the Registrant to be due to possible physical effects (e.g., occlusion at the high soil concentration tested, 1000 mg/kg nominal, 945 mg/kg measured). As a result of this concern, the Registrant formally proposed follow-up investigation in radish (short-term plant toxicity testing) in order to: (1) to confirm the observed growth effects in radish from the previous initial study as reproducible using a definitive study test design involving different soil exposures to evaluate a dose response; (2) to determine a NOEC in radish for growth and emergence and (3) to carry out a definitive PNEC assessment related to the terrestrial compartment (e.g., soil) that is not possible with the currently available data.

 

ECHA has agreed with the justification provided above by the Registrant and consequently has requested a follow-up short-term terrestrial plant toxicity study in radish (OECD 208 guidelines) be carried out with the registered substance, reaction products of 1-decene, 1-dodecene and 1-octene, hydrogenated.  The Registrant has recently completed the follow-up definitive radish study and the new findings are updated in IUCLID and the CSR and summarized in the discussion below.

 

Based on the available terrestrial plant read-across “analogue” data (ExxonMobil Biomed Sciences Lab., 2009b) and the recent follow-up definitive dose-response study in radish (ExxonMobil Biomed Sciences Lab., 2013) , the registered substance would not be expected to have any adverse effect on seedling emergence or growth in plants. The recent follow-up findings in radish clearly demonstrated no adverse effects or dose-response effects on growth and provided a 14-day NOEC >935 mg/kg (measured) for both emergence and growth. Read-across data established a 14-day NOEC > 943 mg/kg in wheat and a 14-day NOEC > 962 mg/kg in mung bean plants for both emergence and growth for the registered substance. Collectively, the follow-up radish and the read-across short-term terrestrial plant studies indicated registered substance would not be expected to cause any acute toxicity to terrestrial plants in terms of seedling emergence or growth. No dose response in these endpoints was observed in radish from the lowest 100 mg/kg nominal to the highest 1000 mg/kg nominal soil exposure groups. As discussed previously, the registered substance is also not expected to cause any short-term toxicity to terrestrial macro-organisms like the earthworm (14-day NOEC > 890 mg/kg soil dw). Therefore, given the limited information available currently, it is not possible to carry out any definitive PNEC assessment at this time related to the terrestrial compartments or to determine whether exposure assessments or additional long-term terrestrial organism toxicity testing are warranted. 

Read-across Justification (Analogue Approach):

 

Several criteria justify the use of the read-across approach to fill data gaps for the registered substance using the 1-decene dimer, hydrogenated constituent substance. These substances are all hydrogenated poly alpha olefins, i.e., branched saturated paraffins or alkanes produced by oligomerization of 1-octene, 1-decene, and/or 1-dodecene. As described in the read-across justification appended to the CSR, these substances (being branched saturated alkanes) are similar in molecular structure, physicochemical properties, use, and manufacturing processes.Especially relevant to aquatic toxicity are the comparable water solubilities (i.e., very poorly water soluble, < 0.001 mg/L or < 1 ppb) and partition coefficients (log Kow >10). Based on these unifying considerations, the slight difference in carbon number among these analogues is not expected to impact their aquatic toxicity. Therefore, it is scientifically reasonable to predict the ecotoxicological properties for the registered substance from the properties determined for the read-across analogue(s). These substances are related branched alkanes having analogous or homologous molecular structure and very similar inherent physico-chemical properties andare thus expected to exhibit similar toxicological effects.

 

The nature of the read-across approach utilized here is aligned with the “analogue approach” as described in section R.6.2.3 of the ECHA document ‘Guidance on Information requirements and chemical safety assessment Chapter R.6: QSARs and grouping of chemicals’ (ECHA, 2008e). The “analog” similarity among molecular structure and molecular weight which provides the basis for the read-across justification is scientifically founded and therefore adequately clarifies why the properties of the registered substance may be predicted from the properties of the read-across substance(s) and more specifically, why the data submitted for 1-decene dimer hydrogenated (C20) are appropriate for the purposes of read-across assessment of the registered substance which contains similar molecules with carbon numbers in the ranges of 18-24 carbon atoms (containing at least 60% C20 components). Long-term Terrestrial Plant Toxicity (Weight of Evidence) - see full document for Environmental WoE for Long-Term Terrestrial Plant Toxicity in Section 13 of IUCLID as an attachment.,

 

There are no key studies for long-term terrestrial plant toxicity for the registered substance, the reaction products of 1-decene, 1-dodecene and 1-octene, hydrogenated. However, there are available key studies for short-term terrestrial plant toxicity that demonstrate the registered substance causes no toxicity or adverse effect to plants. There are several long-term terrestrial studies which show no toxicity to soil micro-organisms (e.g., nitrification) and no toxicity to earthworms (e.g., reproduction) that are informative and should be considered in an overall weight of the evidence and as supporting information for the model presented below. Also there are available EqP-TLM framework data (CONCAWE 2013) that provide key information assessing the potential non-toxicity of the registered substance in terrestrial plants (to be discussed more fully below).

 

The purpose of this weight of evidence (WoE) assessment is to address whether all key data or relevant information available for consideration have been applied to make an assessment of the potential long-term terrestrial plant toxicity of the registered substance without the need for further unnecessary testing. 

 

Key data elements or information under consideration in this overall WoE assessment include:  

 

1.     The Equilibrium Partitioning-Target Lipid Models (EqP-TLM) approach developed by CONCAWE (2013) to correlate environmental toxicity with structure as well as physico-chemical properties specifically log Kow /water solubility, log Koc and bioavailability to predict aquatic and terrestrial toxicity of non-polar organics.  This framework is described. 

 

2.     Application of the EqP-TLM approach to the registered substance can predict lack of long-term effects in terrestrial plants and provides WoE support that long-term testing in plants is not necessary CONCAWE (2013).  

 

3.     Short-term terrestrial plant toxicity data showing no adverse effects. It should be noted that no acute and no chronic adverse effects were observed in the terrestrial earthworms studies for the registered substance, which provides acute to chronic correlation support (e.g., owing to similar mode of action). On the basis of this data set, chronic adverse effect would similarly not be expected in plants.

 

4.     Relevant long-term terrestrial studies such as soil microorganism/nitrification (OECD 216) and earthworm reproduction (OECD 222) studies showed no toxicity to other soil organisms for the registered substance. In addition, no acute or chronic toxicity have been observed in testing with aquatic organisms. Given the whelming extent of non-toxicity findings for the registered substance across the spectrum, there is no need or justification to further investigate long-term effects.    

 

Conclusions:

 

This scientific robust WoE evaluation has assessed and demonstrated that the chronic terrestrial plant toxicity as the additional long term terrestrial toxicity testing (e.g., plants) is not scientifically necessary. The use of EqPM-TLM framework approach (CONCAWE 2013) based on the log Kow characteristics of the registered substance provides sufficient WoE information to assess whether long-term terrestrial testing is needed. The low water solubility limitations and low bioavailability of the registered substance are likely mechanisms contributing to the expected non-toxicity in plants and in other terrestrial organisms (e.g., soil microbes, earthworms) for the registered substance in the EqP-TLM assessment.  Therefore, the registered substance with it very low water solubility and high log Kow >10 would be expected not to cause any adverse effects in long-term plant toxicity test based on EqP-TLM framework. This lack of predicted long-term toxicity in plants for the registered substance would be consistent with the lack of adverse effects observed in the acute plant toxicity studies for the registered substance or its components (NOEC > 1000 mg/kg nominal ) in mung bean, wheat and radish (see Section 7.2.1.2 of CSR ). In conclusion, further long-term plant toxicity testing is not necessary and is not scientifically justified since the EqP-TLM approach already indicates that the registered substance is not expected to cause long-term adverse effects to plants.

 

Furthermore, other WoE data provided in this document include the fact that the registered substance already has been shown to not cause any short-term toxicity to terrestrial plants and there are other relevant long-term terrestrial data for the registered substance showing no chronic effects to soil microorganisms (i.e., no effect on soil nitrification microbes) and to soil earthworms (i.e., no effects on reproduction, survival, growth). In addition, there are extensive data showing no adverse acute or chronic effects to aquatic organisms. Lastly, the registered substance is comprised of long-chain C18-C24 saturated branched alkanes that are considered as inherently inert and unreactive with no functional reactive group or structural alerts which would indicate hazard or adverse effect potential in the water and terrestrial environments.  In conclusion, long-term plant toxicity testing is not necessary and adverse effects would not be expected in plants based on EqP-TLM.