2-methylpentane-1,5-diamine

Endpoint summary

Description of key information

Studies on terrestrial toxicity were performed with source substance HMD (CAS No. 124-09-4) and found to be applicable to the target substance (see read-across report in IUCLID section 13).

With regard to results on earthworms (OECD 222; GLP; RL1; 2017), the most sensitive endpoint was reproduction:

EC10 (56 d, earthworm reproduction) = 176.1 mg test item/kg soil (dw) (95% Confidence limits (CL) = 151.0 – 202.3 mg test item/kg soil (dw).

With regard to nitrogen tranformation by soil organisms (OECD 216; GLP; RL1; 2017), HMD had no adverse effects on N-transformation in lucerne amended soil during 28 days at test item concentrations of up to and including 1000 mg/kg soil dry weight. ICx (28 d; nitrogen transformation) > 1000 mg/kg soil dry weight.

Additional information

The submission substance is of low lipophilicity. However, due to its positive charge it is prone to bind on negatively charged solid matter and binding to soil and - to a lesser degree - sediment was observed for read-across source substance HMD (CAS No. 124-09-4; OECD 106) and found to be relevant for the target substance MPMD (see read-across report in IUCLID section 13). In spite of this, the submission substance proved to be readily biodegradable fulfilling the 10-day window requirement with total nitrification within 28 days, such that accumulation in soil or sediment is not anticipated. This is confirmed by the study on nitrogen-transformation by soil microorganisms (OECD 216; RL 1) performed with read-across source-substance HMD: independently from the test item concentration (between 62.5 and 1000 mg/kg soil dry weight), consistently between 50% and 64% of the test item borne nitrogen was transformed to nitrate within 28 days, in addition to the nitrate stemming from amending soil with Lucerne meal containing nitrogen. As cleavage of the C-N-bonds is a prerequisite for nitrification and will reduce adsorption and increase bioavailability; and considering in addition ready biodegradability; this allows for concluding on rapid mineralization of MPMD within natural soil.

The PNEC soil estimated by the equilibrium partitioning method (EPM) using experimentally determined adsorption data resulted in a value of 314.5 mg/kg soil dw. Taking into account the required additional factor of 10 for adsorbing compounds according to ECHA guidance R.10, this PNEC (31.4 mg/kg soil dw) should be protective for terrestrial organisms exposed predominantly via the soil pore water. However, internal exposure of terrestrial organisms incorporating solid matter might be a concern as well as exposure to bound material by surface contact. To account for this, a chronic Earthworm Reproduction Test according to OECD 222 was performed with read-across source-substance HMD. Earthworms incorporate soil particles and thus are exposed both via pore water and internally. By their thin cuticle they are also prone to be affected by exposure via surface contact. Therefore, this test can be considered as appropriate to cover routes of terrestrial exposure not accounted for by EPM. Further, this is in line with ECHA guidance R.7c, section R.7.11.6.3: based on Table R.7.11-2, MPMD (like source substance HMD) is assigned a hazard category 3 due to its adsorptive properties. Thus, according to the ECHA Guidance, a confirmatory long-term soil toxicity test must be performed (e.g., with the most sensitive organism group as indicated from aquatic toxicity data). On this basis, invertebrates are the most sensitive species and a chronic test on earthworms according to OECD 222 is confirmed to be well appropriate. At last, according to ECHA guidance R.7c, the intrinsic properties of soil microbial communities are not addressed through the EPM extrapolation method. Therefore, a study on nitrogen transformation by soil microorganisms according to OECD 216 was also performed with read-across source substance HMD. Both test results (OECD 222 and OECD 216) were found to be applicable to target substance MPMD (see read-across report in IUCLID section 13).

Regarding results on earthworms (OECD 222; GLP; RL1; 2017), the most sensitive endpoint was reproduction:

EC10 (56 d, reproduction) = 176.1 mg test item/kg soil (dw) (95% Confidence limits (CL) = 151.0 – 202.3 mg test item/kg soil (dw).

Regarding nitrogen transformation by soil organisms (OECD 216; GLP; RL1; 2017), the test item had no adverse effects on N-transformation in lucerne amended soil during 28 days at test item concentrations of up to and including 1000 mg/kg soil dry weight. Due to lack of any adverse effects, inhibitory concentrations (ICx) could not be calculated. Consequently, ICx are considered to be higher than 1000 mg/kg soil dry weight which was the highest tested concentration. Accordingly, LOAEC and NOAEC are > and ≥ 1000 mg/kg soil dry weight, respectively.

Given those long-term results on earthworm and soil microorganisms, PNEC_soil is derived from these data in parallel to the EPM-method, as required according to ECHA guidance R.7c, sections R.7.11.5.3 and R.7.11.6.3. From these experimental data (two trophic levels, i.e., detrivors and consumers; AF 50 according to ECHA guidance R.10), a terrestrial PNEC of 3.52 mg/kg soil (dw) results. This value is lower compared to the terrestrial PNEC obtained from EPM (31.4 mg/kg soil dw after application of additional factor of 10) and is therefore used for environmental risk assessment. As there is no indication of risk from these confirmatory long-term soil toxicity results (PEC/PNEC_exp <1), no further toxicity testing for soil organisms is required (ECHA guidance R.7c).