Abstract:
Unilever product ingredients are discharged into the environment via a number of routes, in
many regions of the world there is a lack of municipal waste water treatment and the
discharge of chemicals directly into the environment in the presence of untreated sewage is a
major pathway. An absence of data on the behaviour of the fate and effects of chemicals
under such conditions requires overly stringent and unrealistic assumptions when assessing
risk (e.g. no biodegradation is assumed). Traditional risk assessment fails since water quality
is compromised by pollutants associated with raw sewage (e.g. BOD and ammonia) and the
relevance of the ‘standard’ risk assessment approach has thus been questioned. An alternative
risk assessment model, based on the ‘impact zone’ concept, has been proposed for direct
discharge conditions. In this model, chemicals are assessed in terms of their predicted
environmental concentration (PEC) at the end of an impact zone, within which the ecosystem
is impacted by the pollutant, free ammonia, and beyond which it is not. Linear alkylbenzene
sulphonate (LAS) was used a model compound to understand the fate of materials classified
as readily biodegradable in this scenario. Batch and dynamic test systems simulating
conditions associated with untreated discharge, confirmed that LAS was degraded quicker
than the general organics present in settled sewage and that beyond the defined ‘impact zone’
it is extensively removed.
Predicted no effect concentrations (PNECs) can also be generated for chemicals on the
inhibition of key microbial processes (biological oxidation and nitrification) which are
essential in rivers for self purification. A variety of detergent ingredients (ranging from
readily biodegradable to anti-bacterial) were investigated in short term toxicity
tests. The tests produced a range PNECs and confirmed that these ingredients can show
selective inhibition towards heterotrophic or autotrophic bacterial populations. All of the
PNECs generated were above the PEC for these ingredients.
