Reaction mass of diiron carbide, diiron phosphide and triiron phosphide

Long-term toxicity to fish

Administrative data

Endpoint:

fish early-life stage toxicity

Data waiving:

study scientifically not necessary / other information available

Justification for data waiving:

other:

Justification for type of information:

Dissolved concentrations from a 28d-T/Dp test at a loading of 1 mg/L were the starting point for the assessment of long-term environmental effects (for daphnia and fish) of a sparingly soluble substance such as Fe3P. As explained in section 2 of this document, a ‘classic’ assessment approach is not possible for this substance due to several reasons:
• the complexity of P-speciation
• the low levels of dissolved P make the identification/quantification of all individual species impossible
• the lack of relevant ERVs for all individual P-species forms
• it is technically not feasible to make an equivalent solution in standard test medium with regard to P-speciation by using soluble salts

The only remaining option for the required assessment is to conduct the tests directly in T/D-medium. This approach was successfully applied for acute toxicity testing (7-dT/Dp medium with loadings of 10 and 100 mg/L), but conducting long-term tests would need large amounts of continuously generated T/Dp medium, and the production set-up as well as the analytical monitoring of all test solutions would come at an excessive cost. Such cost could only be justified if there are reasonable indications that long-term toxicity is likely to occur.

All Fe3P data that are currently available, however, demonstrate that this is not the case:
• No acute toxicity of Fe3P was noted for the fish P. promelas (96h-LC50 >100 mg/ Fe3P in TDp medium) and the green algae R. subcapitata (EC10 >100 mg/ Fe3P in T/Dp medium; algal growth stimulation compared to the control). It can thus be concluded that none of the released P-species (known and unknown forms) at a loading of 100 mg/L can cause an acute adverse effect, and dissolved levels are within the range of concentrations that are found in natural surface waters.
• Phosphine is a toxic P-compound that is formed upon dissolution of some P-compounds; the tests of phosphine-evolution in T/Dp medium at pH 6 showed that no phosphine could be detected after 7 days at a loading of 400 g/L (Klimmek and Schneider, 2021; study included in section 4.8 of the dossier). This exposure period is typically used for assessing acute toxicity, whereas 28 days is representative for long-term testing. This is a factor of four shorter, but at the same time an extreme high loading was assessed, i.e. 400 g/L, or 4.0 x 10^8 times higher than the reference loading of 1 mg/L for assessing long-term effects.

The loading of Fe3P in this phosphine evolution test is half a billion times higher than what needs to be considered for long-term assessment purposes; since no phosphine is detected in this test design after 7 days, it was be concluded that this P-species form is not formed when Fe3P dissolves in water under environmentally relevant conditions. Read-across to non-hazardous P-compounds is justified and a long-term test with Fe3P can be waived on the basis that this is scientifically not necessary.