Alkali salt of sulfonated aryl azo amino sulfonyl aryl azo sulfonyl aryl azo aryl sulfonate

Endpoint summary

Additional information

It should be noted that the test substance is not considered as posing a hazard to the aquatic environment.

The test substance, Reactive Brown DYHY 0331/0334 , is a solid under all environmental conditions and is highly soluble in water. It has a low volatility (based on the high melting / boiling point and high molecular weight) and a low affinity for soil / sediment (based on the partition coefficient value of log Kow < -6 and the calculated adsorption coefficient of log Koc < - 0.9). As such, any environmental release will result in virtually all of the substance compartmentalising into water compartments, with little release directly to atmosphere or compartmentalising to soil/sediment compartments.

Any potential exposure to the environment is predicted to result in rapid redistribution to water; due to its low volatility, high water solubility and partitioning values indicates that the majority of the substance would eventually partition to water rather than to soil and sediment should it be released to the environment.

A Level III fugacity model was conducted in the US EPA EPISUITE which assumes steady-state but not equilibrium conditions. The Level III model in EPI Suite predicts partitioning between air, soil, sediment and water using a combination of default parameters and various input parameters. This model has been used to calculate the theoretical distribution of the highest % component substance between four environmental compartments (air, water, soil, sediment) at steady state in a unit world.

Partitioning model Reactive Brown DYHY 0331/0334

 

Compartment

Distribution [%]

Half-life [h]

			DYHY0331	DYHY0334		DYHY0331	DYHY0334
Air			2.05E-005	3.4E-006		12.7	5.7
Water			0.992	0.619		4.32E+003	4.32E+003
Soil			58	53		8.64E+003	8.64E+003
Sediment			41	46.3		3.89E+004	3.89E+004

It is proposed that although the majority of the substance distributes to the soil/sediment compartments within the model, the high solubility in water indicates that the substance is more likely to distribute to water – e. g. soil pore water.

This assumption is confirmed by the model for the STP Overall Chemical Mass Balance in the US EPA EPI SUITE, which shows that 98% of the influent of the dye is in the water phase:

STP Overall Chemical Mass Balance

 

g/h

mol/h

percent

	DYHY0331	DYHY0334	DYHY0331	DYHY0334	DYHY0331/0334
Influent	1.00E+001	1.00E+001	9.1E-003	8.4E-003	100.00
Primary sludge	2.50E-002	2.50E-002	2.3E-005	2.1E-005	0.25
Waste sludge	1.50E-001	1.50E-001	1.4E-004	1.3E-004	1.50
Primary volatilization	2.02E-024	3.66E-025	1.8E-027	3.1E-028	0.00
Settling volatilization	5.51E-024	9.98E-025	5.0E-027	8.3E-028	0.00
Aeration off gas	1.36E-023	2.46E-024	1.2E-026	2.1E-027	0.00
Primary biodegradation	1.76E-003	1.76E-003	1.6E-006	1.5E-006	0.02
Settling biodegradation	5.27E-004	5.27E-004	4.8E-007	4.4E-007	0.01
Aeration biodegradation	6.93E-003	6.93E-003	6.3E-006	5.8E-006	0.07
Final water effluent	9.82E+000	9.82E+000	9.0E-003	8.2E-003	98.15
Total removal	1.85E-001	1.85E-001	1.7E-004	1.5E-004	1.85
Total biodegradation	9.22E-003	9.22E-003	8.4E-006	7.7E-006	0.09

Reactive Brown DYHY 0331/0334 displays a low ready biodegradability in that it achieved 6% biodegradation in a ‘Manometric Respirometry Test’. In a test for inherent biodegradability (Modified MITI Test (II)), the test substance was primary biodegradable (45% based on BOD; 49% DOC removal) but not ultimate biodegradable, and was hence not considered to be inherent biodegradable. The substance is expected to hydrolyse rapidly under normal environmental conditions. Experimental studies on hydrolytic effects demonstrated that the substance does undergo rapid hydrolysis at environmentally relevant pH (pH 7: t_½= 18.6 d (DYHY0331) and 10.4 d (DYHY0334) at 20°C; pH 9 < 1 d (both components) at 20°C), indicating the potential for significant removal by hydrolysis. At use conditions during dyeing (pH > 10 at ≥ 60°C) the substance is hydrolytically unstable. At 50°C and pH 9, more than 90% of the substance was degraded at the first measure point of 120 hours. As such, degradation is anticipated via this route. Studies on direct phototransformation in water are not available but it was found that the sulfonated azo dyes can be destroyed by UV photooxidation process (Saliha 2004). The kinetics of the degradation depends on the azo, benzene and naphthalene groups of the dyes. It was found that the first step of the degradation is related to cleavage of azo bond of the molecule and naphthalene ring which leads to further degradation until complete mineralization. It is concluded therefore, that abiotic processes would contribute significantly to the depletion of the substance within the environment.

Reactive Brown DYHY 0331/0334 has an estimated log Kow of < -6. This value indicates that possible bioaccumulation in the food chain is not anticipated. Given the fact that the substance is subject to hydrolysis at biologically relevant pH, it is anticipated that bioaccumulation of the substance itself would not occur, as hydrolytic effects in association with metabolic effects would result in removal of the substance. Based on its high water solubility, low partition coefficient and fairly rapid hydrolysis rate at environmentally relevant pH, it can be concluded that it is unlikely that Reactive Brown 0331/0334 could potentially be persistent within the environment.

Adsorption to soil is deemed to be low, based on the very low partition and adsorption coefficient values and high water solubility. Such a low potential indicates that the substance is unlikely to bind tightly to soils and sediments and instead partition almost exclusively to water. As such, significant exposure related effects to sediment and soil dwelling organisms are considered to be negligible.

Based on its high water solubility and low partition coefficient it can be concluded that it is unlikely that Reactive Brown DYHY 0331/0334 could potentially be persistent within the environment in its registered form. Abiotic effects within the environment will result in eventual removal from the environment and hence significant contact with the organisms in the food chain can considered to be minimised.

Finally, Reactive Brown DYHY 0331/0334 demonstrates low toxicity in aquatic organisms and mammalian studies therefore in the event of exposure to environmental organisms, effects due to secondary poisoning can be excluded.