There should also be a knowledge of the sensitivity of the test organisms to un-ionized ammonia and salts (e.g. salinity or chloride), as these components often occur at high concentrations in untreated landfill leachate (Kjeldsen et al., 2002) and they might confound the assessment of hazard caused by persistent pollutants (Postma et al., 2002 and Lahr et al., 2003).