1,4-Benzenediamine, N,N'-mixed Ph and tolyl derivs.

Bioaccumulation: aquatic / sediment

Description of key information

Key study - exposure via the diet: : bioaccumulation study in rainbow trout with radiolabeled R-898, K2, GLP, OECD guidelines followed where possible.
* BMFL (lipid normalized growth corrected biomagnification factor): 0.174
* BMFK (growth corrected dietary kinetic biomagnification factor): 0.065
* Fish-growth corrected half life of 4.58 days.

Key value for chemical safety assessment

BCF (aquatic species):

2 107 dimensionless

BMF in fish (dimensionless):

0.174

Additional information

The bioaccumulation potential of DAPD is assessed in fish exposed via the water as well as via the diet.

The bioaccumulation study with exposure via the water (Tadokoro, 1998) is considered to be unreliable based on the following observations:

1) Due to the tendency of DAPD to adsorb to glass surfaces and organic matter, difficulties were faced with maintaining a stable test substance concentration. As a result, the validity criterion regarding the measured concentrations of the test substance in the water is not fulfilled.

2) The reliability of the BCF values calculated in this aquatic bioaccumulation study is low due to:

i)    Only two fish replicates per sampling occasion,

ii)  Variations in the measured concentrations of the test substance in the water exceed the allowed level of variation described in the OECD guideline, and

iii) High variations in the measured concentrations of the test substance in the two fish at each sampling occasion were observed where concentrations up to 50% greater were seen in the second fish at that sampling occasion.

3) The BCF values that are calculated from the aquatic bioaccumulation study are overestimates due to a combined exposure of the test fish via the food and the water.

 

Therefore, based on the observed deviations from the OECD 305 guideline and on the physico-chemical properties indicating the risk for combined exposure of the fish via both aquatic and dietary routes, the BCF study by Tadokoro is considered to be not reliable and should be disregarded in the assessment of the bioaccumulative properties of DAPD.

 

The dietary bioaccumulation study by Vaughan was conducted according to the OECD 305 guideline published in October 2012 without any significant deviations from the protocol.

For substances with a physico-chemical profile including low water solubility and a high tendency for sorption to soils, sediment, and other solids, a dietary bioaccumulation study is recommended by OECD. More reliable results will be obtained for these substances when bioaccumulation is examined following exposure via the diet as the technical difficulties associated with the formation of stable test substance concentration in the water are avoided.

 

For the dietary bioaccumulation experiment, radio-labelled R-898 was mixed with the fish feed. Rainbow trout were dosed with this feed for 14 days, followed by a 14 day depuration period. The presence of the radioactive tracer in the exposed fish was examined using liquid scintillation counting.

 

A growth-corrected depuration rate constant of 0.151/day was derived from the measured concentrations of DAPD equivalents in fish body tissue during depuration. A fish growth corrected half life of 4.58 days, substance assimilation efficiency of 0.491 and growth corrected/lipid normalised growth corrected kinetic biomagnification factors ( 0.0065 and 0.174, respectively) were calculated.

An estimated bioconcentration factor of 2107 (fish body tissue) was also determined. In order to determine a bioconcentration factor an uptake rate constant is estimated based on fish weight and using key assumptions, such as the uptake rate constant obeying first order kinetics. While an estimated bioconcentration factor may be useful in predicting the bioaccumulative nature of a test substance, the biomagification factor is considered a more appropriate measure in the case of a dietary bioaccumulation test.