TR 054 – Assessment of the Biodegradation of Chemicals in the Marine Environment

TR 054 : Assessment of the Biodegradation of Chemicals in the Marine Environment | August 1993

Several test methods assessing the biodegradation potential of a chemical has been developed and validated for freshwater situations. Internationally accepted standard methods are now available and the data available covers a wide range of chemicals. In contrast to freshwater situations no generally accepted methods are known to estimate the biodegradation potential of chemicals in marine situations. The literature research on marine biodegradation reveals that apart from a few examples research has focused on degradation of crude oil and petroleum derivatives.

OECD published recently a set of "Marine Ready Biodegradability Tests" which may, to a certain extent, predict the fate of a chemical in heavily polluted estuaries. It is doubtful whether the result obtained from these test guidelines would be representative for open sea or coastal situations where conditions considerably differ from those in freshwater or estuarine situations.

The marine environment is characterised by a low concentration of nutrients (P,N) and organic substrate. Except for the surface microlayer, where large populations of marine microorganisms have been recorded, the bacterial counts are orders of magnitude lower than those observed in freshwater situations. When developing a biodegradation test for marine situations both physico-chemical and biological parameters which are typical for this environment should be maintained. This implies a low test concentration which precludes the monitoring of the fate of a chemical using non-specific analytical methods.

A strategy is outlined and schematically represented as a tier approach to assess the hazard of a chemical which may reach the marine environment. The test strategy is designed to eliminate as far as possible unjustified testing.

Biological processes for biodegradation in freshwater and the marine environment do not differ. Thus, in theory, those chemicals which are readily biodegradable in freshwater will also degrade under marine situations. The available information only supports this conclusion with regard to ready biodegradability.

Marine biodegradability tests should be carried out using test protocols simulating the situation and the receiving environment as closely as possible. Proposals for the design of possible test protocols are described.

It is recommended that, when more knowledge is obtained about marine biodegradation, the strategy should be reconsidered.