p-phenylene diisocyanate

Short-term toxicity to fish

Link to relevant study record(s)

Reference

Endpoint:

short-term toxicity to fish

Type of information:

read-across from supporting substance (structural analogue or surrogate)

Adequacy of study:

key study

Justification for type of information:

1. Source and target substances
The substances m-tolylidene diisocyanate (CAS No 26471-62-5, consisting of 80% tolylidene 2,4-
diisocyanate and 20% tolylidene 2.6-diisocyanate, hereafter referred to as TDI,source) and pphenylene
diisocyanate (CAS No 104-49-4, hereafter referred to as p-PDI, target) each consist of a
diisocyanate substituted benzene ring. The substituents on the phenyl ring are almost identical in
both cases, with the TDI being substituted in a meta-fashion with the two isocyanate groups, while
the p-PDI features the substituents in a para-fashion. Aside from this, the TDI features an additional
methyl substituent on the phenyl ring, which is absent in the p-PDI.
2. Description of the scenario
In the ECHA RAAF document 6 different read-across approaches are described in the form of
“scenarios”. The scenarios thereby categorize the type of read-across approach used to allow a
systematic assessment of the crucial scientific aspects. Each scenario comprises different
“assessment elements”, which address different scientific considerations deemed crucial to judge the
validity and the reliability of read-across.
In the present case, the read-across approach of m-tolylidene diisocyanate (TDI) and p-phenylene
diisocyanate (p-PDI) corresponds with scenario 2.
This scenario covers the analogue approach (read-across is employed between a small number of
structurally-similar substances; there is no trend or regular pattern on the properties) for which the
read-across hypothesis is based on qualitative similar properties of the compounds.

3. Read Across Hypothesis
The read-across approach should be used for data gap filling of p-phenylene diisocyanate (p-PDI)
using fate, ecotoxicitiy and human health toxicity studies of m-tolylidene diisocyanate (TDI). Based
on the similar chemical structure and the available experimental data both substances are highly
reactive diisocyanates. The chemical reactions known for the highly reactive diisocyanates (e.g. rapid
hydrolysis to the diamine in aqueous environments, polymerization reactions and reactions with
amines or hydroxyl groups in biological specimens) are reported for TDI (MAK 2003, ECHA 2013)
and can be assumed to take place also when p-PDI enters an organism. Both compounds consist of
a benzene ring and two isocyanate groups. TDI is substituted in a meta-fashion with the two
isocyanate groups, while the p-PDI features the substituents in a para-fashion. The differences in the
substitution pattern (meta versus para) do not lead to a difference in reactivity of the highly reactive
isocyanate groups.
It is reasonable to assume and experimentally verified that both compounds have nearly identical
behavior in physico-chemical and (eco)toxicological studies. Therefore there should be almost no
differentiation between effects of target and source substance.

4. Data Matrix
Please refer to Section 13.2 "Other Assessment reports" for full justification, reference "pPDI+TDI READ ACROSS JUSTIFICATION".

Reason / purpose for cross-reference:

read-across source

Key result

Duration:

96 h

Dose descriptor:

LC50

Effect conc.:

133 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

mortality (fish)

Validity criteria fulfilled:

yes

Conclusions:

The read across for pPDI; is based upon the analogous substances to which basic form, degree of substitution of functional groups is not considered to effect the proposed read across for the endpoint of acute toxicity to fish. Based on the information available for the read across substances, the substance is not expected to be harmful to fish.

Executive summary:

The read across for pPDI; is based upon the analogous substances to which basic form, degree of substitution of functional groups is not considered to effect the proposed read across for the endpoint of acute toxicity to fish. Based on the information available for the read across substances, the substance is not expected to be harmful to fish.

Description of key information

The read across for pPDI is based upon the analogous substances to which basic form, degree of substitution of functional groups is not considered to effect the proposed read across for the endpoint of acute toxicity to fish. Based on the information available for the read across substances, the substance is not expected to be harmful to fish.  Please refer to Section 13.2  "Other Assessment reports" for full justification, reference "pPDI+TDI READ ACROSS JUSTIFICATION".

Key value for chemical safety assessment

Fresh water fish

Fresh water fish

Effect concentration:

133 mg/L