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Toxicity to microorganisms

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Description of key information

Two studies have been carried out on the analogue materials Abacavir Succinate and Abacavir Hemisulphate.

Abacavir Succinate

(Jenkins - 1997) The test material is considered to be of low toxicity to activated sludge.

Abacavir Hemisulphate

(Swarbrick & Smyth - 2004)

The % removal of the test material from activated sewage sludge after 24 hours was considered to be equal to or greater than 97%.

Key value for chemical safety assessment

EC50 for microorganisms:
61 mg/L
EC10 or NOEC for microorganisms:
61 mg/L

Additional information

The studies were carried out on one of the analogue materials. The analogues are considered to be sufficiently similar to the substance of interest (please see attached data matrix and justification in Section 13 for additional details) for them to be used for the purposes of health and environment risk assessments.

Both studies were carried out to GLP however only one study was carried out to OECD Guidelines (Jenkins - 1997). Based on this the study by Jenkins was considered to be the more reliable of the two studies and was therefore allocated as the key study of interest.

Jenkins (1997)

Introduction:

The objective of this study was to assess the effects of 1592U89 on sewage micro-organisms by measuring the rate of oxygen uptake of activated sludge at 20° ± 2°C, in its presence at a range of concentrations. The methods employed were designed to meet the requirements of EC Directive 87/302, 'Biodegradation Activated Sludge Respiration Inhibition test' and OECD test guideline 209, 'Activated Sludge, Respiration Inhibition test'.

Material and Methods:

Samples of activated sludge (suspended solids 1.6 g/L), were exposed to 1592U89 for thirty minutes and three hours. Two tests were conducted: a preliminary screen, at nominal volatile free 1592U89 levels of 0.658, 6.58 and 65.8 mgIL (1,10 and 100 mg/L as the succinate salt) and a fmal limit test in which triplicate vessels contained 1592U89 at a nominal concentration of 65.8 mglL (100 mg/L as the succinate salt). Controls were established at the start and end of each test series and the reference inhibitor 3,5-dichlorophenol (3,5-DCP) was employed in each test at 3.0, 10 and 32 mg/L, as a positive control.

Results:

The results of chemical analysis of the stock solutions of 1592U89 prepared at nominal concentrations of 500 mg/ L, from which test dilutions were prepared, indicated that they were correctly formulated (94 and 92% of nominal).

The results obtained for rates of oxygen consumption of controls and for the three-hour 50% effect concentration (EC50) for 3,5 DCP confirmed that the tests were valid and that the samples of activated sludge employed were sensitive to inhibition.

The test material had no significant inhibitory effect on the respiration rate of activated sludge at any of the concentrations employed in the test. The thirty minute and three hour EC20, EC50 and EC80 of the test material could not therefore be calculated but these must be greater than a 1592U89 volatile free level of 61 mg/L (92.7 mg/L as the succinate salt), which was estimated from stock solution analysis to be present at the highest tested level.

Conclusion: The test material is considered to be of low toxicity to activated sludge.

Swarbrick & Smyth (2004)

A study was carried out on the test material according to "Development of a method for adsorption of dyestuffs on activated sludge" U Pagga and K Taeger.

An aqueous mixture of activated sludge, mineral nutrients and abacavir sulphate (the sole source of carbon) were placed together in conical flasks and stirred and aerated for 24 hours. The adsorption process was monitored by removal of aliquots of the mixture at periodic intervals, centrifuging to remove particulate matter and analysing the supernatant liquid (aqueous phase) for abacavir sulphate.

Measurement of the concentration of abacavir sulphate using high performance liquid chromatography (HPLC) was made at the beginning, during and at the end of the test (0, 3 and 24 hours).

The HPLC measured values were used as the basis for calculating the degree of removal (adsorption) and the distribution coefficient if the results showed that adsorption had taken place. The measurement of elimination in the test vessels allowed no direct differentiation between adsorption and other elimination mechanisms such as complex formation, flocculation, precipitation, sedimentation or biodegradation.

Experimental values

Time (hours)

Test solution contents

Abacavir

Sulphate + sludge

Abacavir

Sulphate (abiotic control)

% Removal from aqueous phase

3

32

<5

24

97

<5

The theoretical concentration of abacavir sulphate in the sludge at the end of the test, by difference, was 8042 mg kg-1. Since the percentage removal from the aqueous phase in the test flask was 97% compared with <5% in the abiotic control, it is considered that the removal of abacavir Sulphate during the study was a biotic process. Assuming that the removal process was adsorption to the sludge, then the biomass-water distribution coefficient (Kb in 1 kg-1) after 3 and 24 hours was estimated to be 154 and 11169, respectively.