Ecotoxicology, toxic endpoints

Notes Ecotoxicological tolerance values are based on die EC20 values for growth toxicity endpoints (shoot dry mass) reported in Tables 12.1 and 12.2. ND = not determined (no data available). 

Note Ecotoxicological tolerance values are based on the EC20 values for reproduction toxicity endpoints reported in Table 12.3. 

In the past few years the use of rotifers in ecotoxicological studies has substantially increased. The main endpoints used are mortality, reproduction, behavior, cellular biomarkers, mesocosms, and species diversity in natural populations [126]. Several workers have used Brachionus calyciflorus for various types of toxicity assessments. Thus, comprehensive evaluation of approximately 400 environmental samples for the toxicity assessment of solid waste elutriates, monitoring wells, effluents, sediment pore water, and sewage sludge was carried out by Persoone and Janssen [127]. The mortality of rotifers hatched from cysts is evaluated after 24 hours exposure. This microbiotest has been commercialized in a Rotoxkit F [128,129]. 

Most of the ecotoxicological (Q)SAR models are based on the identification of substructures of the molecule, the degree to which they contribute to the physical properties of the molecule, and how they may contribute to the observed activity. Depending on the sophistication, the model will initially attempt to identify possible linear relationships between the octanol-water partition coefficient (Kow) and observed toxicity, when the toxicity of an active compound can be explained by its lipophilicity (narcosis effect). (Q)SAR models for narcosis toxicity based on Kow are available for many endpoints and species, have been applied to preliminary screening of substances for which no data are available, and are discussed in more detail in Chapter 3. 

Cairns J, Niederlehner BR, Smith EP. 1992. The emergence of functional attributes as endpoints in ecotoxicology. In Burton GA, Jr, editor. Sediment toxicity assessment. Boca Raton (FL) Lewis Publishers, p 111-128. 

For sublethal responses, the level of resource allocation is essential. The DEB approach offers great promise as a TD model in ecotoxicology. It has been applied to the combination of a toxicant with another stressor (food limitation), but its application to mixtures of toxicants requires further work, and a comparison to dedicated experimental data. The EU sixth framework project NoMiracle has delivered such data, which in time will help develop the DEB mixtures approach to also cover sub-lethal endpoints. 

Jager T, Vandenbrouck T, Baas J, De Coen WM, Kooijman SALM. 2010. A biology-based approach for mixture toxicity of multiple endpoints over the life cycle. Ecotoxicology (doi 10.1007/sl0646-009-0417-z). 

Figure 2 Genetic and cytogenetic endpoints used in genetic ecotoxicology to assess individual-level effects in toxicant-exposed organisms. The large arrow indicates that severe or misrepaired damage to DNA or chromosomes may cause a cell to undergo apoptosis or programmed cell death.

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