Industry is continually synthesizing new chemicals, the regulation of which requires evaluation of the potential danger for humanhealth and the environment. Risk assessment is nowadays considered essential for making these decisions on a scientifically sound basis.
Measures or defined limits include:
no-observed-adverse-effect level (NOAEL), also called no-effect concentration (NEC), no-observed-effect concentration (NOEC) or similarly
There is not much debate on the existence of an NEC,[3] but the assignment of a value is another matter. Current practice consists of the use of standard tests. In the standard tests groups of animals are exposed to different concentrations of chemicals and different effects such as survival, growth or reproduction are monitored. These toxicity tests typically result in a no-observed-effect concentration (NOEC, also called a no-observed-effect level, or NOEL). This NOEC has been severely criticized on statistical grounds by several authors[4] and it was concluded that the NOEC should be abandoned.[5]
A proposed alternative is the use of so-called ECx – the concentration(s) showing x% effect (e.g. an EC50 in a survival experiment indicates the concentration where 50% of the test animals would die in that experiment). ECx concentrations also have their problems in applying them to risk assessment. Any other value for x other than zero may give the impression that an effect is accepted, and this is in conflict with the aim of maximally protecting the environment.[6] In addition ECx values do depend on the exposure time.[7] ECx values for survival decrease for increasing exposure time, until equilibrium has been established. This is because effects depend on internal concentrations,[8] and that it takes time for the compound to penetrate the body of test organisms. However, sub-lethal endpoints (e.g., body size, reproductive output) may reveal less predictable effect patterns in time.[9]
The shape of the effect patterns over time depends on properties of the test compound, properties of the organism, the endpoint considered and the dimensions in which the endpoint is expressed (e.g., body size or body weight; reproduction rateorcumulative reproduction).
Biology-based methods not only aim to describe observed effects, but also to understand them in terms of underlying processes such as toxicokinetics, mortality, feeding, growth and reproduction (Kooijman 1997). This type of approach starts with the description of the uptake and elimination of a compound by an organism, as an effect can only be expected if the compound is inside the organism, and where the no-effect-concentration is one of the modeling parameters. As the approach is biologically based it is also possible by using the dynamic energy budget theory[10] to incorporate multiple stressors (e.g. effects of food restriction, temperature, etc.)[11] and processes that are active under field conditions (e.g. adaptation, population dynamics, species interactions, life cycle phenomena, etc.).[12] The effects of these multiple stressors are excluded in the standard test procedures by keeping the local environment in the test constant. It is also possible to use these parameter values to predict effects at longer exposure times, or effects when the concentration in the medium is not constant. If the observed effects include those on survival and reproduction of individuals, these parameters can also be used to predict effects on growing populations in the field.[13]
Alda Alvarez, O., Jager, T., Nunez Coloa, B. and Kammenga, J.E. (2006). Temporal dynamics of effect concentrations. Environ. Sci. Technol. 40:2478-2484.
Bruijn J.H.M. and Hof M. (1997) – How to measure no effect. Part IV: how acceptable is the ECx from an environmental policy point of view? Environmetrics, 8: 263 – 267.
Chen C.W. and Selleck R.E. (1969) - A kinetic model of fish toxicity threshold. Res. J. Water Pollut. Control Feder. 41: 294 – 308.
Straalen N.M. (1997) – How to measure no effect II: Threshold effects in ecotoxicology. Environmetrics, 8: 249 – 253.
Crane M. and Newman M.C. (2000) – What level of effect is a no observed effect? Environmental Toxicology and Chemistry, vol 19, no 2, 516 – 519
Suter G.W. (1996) – Abuse of hypothesis testing statistics in ecological risk assessment, Human and ecological risk assessment 2 (2): 331-347
Laskowski R. (1995) - Some good reasons to ban the use of NOEC, LOEC and related concepts in ecotoxicology. OIKOS 73:1, pp. 140–144
Hoeven N. van der, Noppert, F. and Leopold A. (1997) – How to measure no effect. Part I: Towards a new measure of chronic toxicity in ecotoxicology. Introduction and workshop results. Environmetrics, 8: 241 – 248.
OECD, Document No 54 of "Series on Testing Assessment", 2006. Current approaches in the statistical analysis of ecotoxicity data: a guidance to application
Kooijman S.A.L.M. (1981) - Parametric analyses of mortality rates in bioassays. Water Res. 15: 107 – 119
T. Jager, Heugens E. H. W. and Kooijman S. A. L. M. (2006) Making sense of ecotoxicological test results: towards process-based models. Ecotoxicology, 15:305-314,
Péry A.R.R., Flammarion P., Vollat B., Bedaux J.J.M., Kooijman S.A.L.M. and Garric J. (2002) - Using a biology-based model (DEBtox) to analyse bioassays in ecotoxicology: Opportunities & recommendations. Environ. Toxicol. & Chem., 21 (11): 2507-2513
Kooijman S.A.L.M. (1997) - Process-oriented descriptions of toxic effects. In: Schüürmann, G. and Markert, B. (Eds) Ecotoxicology. Spektrum Akademischer Verlag, 483 - 519
Kooijman S.A.L.M. (2000) - Dynamic Energy and Mass Budgets in Biological Systems. Cambridge University Press
Heugens, E. H. W., Hendriks, A. J., Dekker, T., Straalen, N. M. van and Admiraal, W. (2001) - A review of the effects of multiple stressors on aquatic organisms and analysis of uncertainty factors of use in risk assessment. Crit. Rev Toxicol. 31: 247-284
Heugens, E. H. W., Jager, T., Creyghton, R., Kraak, M. H. S., Hendriks, A. J., Straalen, N. M. van and Admiraal. W. (2003) - Temperature-dependent effects of cadmium on Daphnia magna: accumulation versus sensitivity. Environ. Sci. Technol. 37: 2145-2151.
Sibly R.M. and Calow P. (1989)- A life cycle theory of responses to stress. Biological Journal of the Linnean Society 37 (1-2): 101-116
Hallam T.G., Lassiter R.R. and Kooijman S.A.L.M. (1989) - Effects of toxicants on aquatic populations. In: Levin, S. A., Hallam, T. G. and Gross, L. F. (Eds), Mathematical Ecology. Springer, London: 352 – 382
