NOEC values

In a continual biocoenosis test (Riverine biocoenosis model) for LAS the biocoenotic NOEC value of >0.65 mg/L has been determined. The test was carried out with a starting concentration of 1.1 mg/L LAS/L over a period of 5 weeks. The NOEC value represents the effect caused by the original detergent and the effects caused by the catabolites as well [297]. The NOEC value shows that biocoenosis reacts more sensitively to compounds than the most sensitive laboratory species, which according to general opinion should not be generalized. 

The bacterial toxicity was measured according DEV, DIN 38412, L3 (TTC(2,3,5-triphenyl-2/7-tetrazolium chlorid) test). The result gives an EC50 (effective concentration) varying between 2290 and 14700 mg/L, and estimated NOEC values in the range of < 10 to 100 mg/L [3.223],... 

Chemical analyses are an indispensable complement to ecotoxicological investigations, but they are not directly integrated in the application of the pT-scale for industrial effluent assessment. Performed in parallel, assessment of chemical substances is governed by a set of criteria, which are derived from ecotoxicological threshold (NOEC) values, in order to derive quality objectives or standards. When bioassay and chemistry results are both available for effluent assessment, they should be ranked equally. For determining the overall hazard of wastewaters, the most conservative information with respect to aquatic health will serve as the yardstick to ensure environmental protection. 

Thus far, quality objectives for chemical substances are derived from the most sensitive organisms in acute and chronic toxicity test batteries that determine NOEC values for different trophic levels. The pT-method similarly determines specific sample dilution levels that are devoid of adverse effects toward (micro)organisms of a standardized test battery. Common to both approaches is the more frequent use of water-column test organisms as opposed to benthic-dwelling organism that reflect more intimate contact with sediment. This practice is primarily based on the fact that standardized bioassays capable of appraising sediment porewaters and elutriates are presently more numerous than solid-phase tests for whole-sediment assessment. As more of these latter tests become developed and standardized (see Chapters 12 and 13, volume 1 of this book on amphipod and chironomid tests), their more frequent use will contribute to a better understand of the toxic effects of sediment-bound contaminants. 

As an example, 2,4-dichlorophenol (2,4-DCP) is an acidic compound with a pA"a of 7.68 and a K0Wni of 3.06 (Mackay et al. 1997). Consultation of the USEPA Ecotox database reveals a chronic reproduction toxicity NOEC value for Daphnia... 

An analysis of regularities observed in species sensitivity distributions (SSD) fitted on acute and chronic aquatic toxicity data for a large number of organic and inorganic toxicants is provided by De Zwart (2002). The log-logistic sensitivity model he used is characterized by the parameter a, which is the mean of the observed loglO-transformed L(E)C50 or NOEC values over a variety of test species, and /3, a scale parameter proportional to the standard deviation of the loglO-transformed... 

Jagoe RH, Newman MC. 1997. Bootstrap estimation of community NOEC values. Ecotoxicol 6 293-306. 

Adopting the ideas proposed by Wurgler and Kramers (1992) and Kurelec (1993), it is proposed that the setting of water or sediment PNEC values for genotoxins should be based on sublethal biological endpoints expressed as statistically robust ECx or NOEC values. In practice, this could include the in vivo measurement of reproduction, development, growth, or specific cytogenetic macrolesions (namely, micronuclei, aneuploidy, and chromosomal aberrations) since these are known to relate to adverse phenotypic outcomes (Brusick 1987 Jha 2004). 

NOTE 2a Chronic toxicity band based on NOEC values in mg/l for fish or Crustacea or other... 

Crane and Newman (2000) also examined the EC values corresponding to NOEC values. In one instance they examined nine sets of round-robin tests for a fish growth toxicity test. The median NOEC value corresponded to an EC level of 10.5%. However, the ranges were large. When LAS was tested, the EC values corresponding to the NOEC ranged from 3.4 to 38.4% and for DCA it ranged from 3.3 to 24.1%. 

Witte et al. determined that subtoxic concentrations of membrane-damaging compounds enhanced the cytotoxicity of hydrophilic xenobiotics (foreign compounds) J11 The data reported show a linear relationship between the logarithm of the no observed effect concentration (NOEC) and K)w values the higher the K, the lower the log NOEC value and greater the toxicity of the mixture. The data in Table 3.3 show Kjw and NOEC in millimoles (mM) for 2,4-dichlorophenoxyaceetic acid (2,4-D). The sole deviant from the relationship, tributylamine, is explained by its extremely low membrane-damaging properties relative to its lipophilicity. 

Table 3.3 K and NOEC Values for Various Compounds Combined with 2,4-D[n°...

Species sensitivity distributions (SSD) on the basis of NOEC values in the literature were used to calculate the toxic pressure (TP an effect value) from the presence of contaminants in the soil or in the pore water (Rutgers et al., 2001 Posthuma et al., 2002). The effect of the contaminants was corrected for the contaminant levels in the local reference samples (field A) ... 

Table 12.1. NOEC values for various species at which alkane sulfonates show no biological activity...

A growing importance is dedicated to chronic toxicity, which describes the harmful properties of a substance which are demonstrated only after a long-term exposure in relation to the live span of the test organism. This is usually expressed by either the LOEC or NOEC values. 

A knowledge of chronic and sub-acute toxic effects is the basis of a risk-assessment procedure which is closer to natural conditions. It is decisive to know what concentration of surfactant causes no observable effects any more. For the quantitative description of a chronic exposure situation, the NOEC value is used. By the eventual use of additional safety factors a so-called PNEC (predicted no effect concentration) value can be derived. The latter describes a situation where in the environment no deleterious effects should be expected any more. Aquatic toxicity and biological degradation are closely connected with each other insofar as a... 

Under the aspects of acute and chronic aquatic toxicides, amphoteric surfactants display a behaviour which is quite similar to the other groups of surfactants, with disodium cocoamphodiacetate being less toxic against fish and daphnids than cocamidopropyl betaine, according to the data presented in Table 22.22. All NOEC values are below 1 mg/1, with daphnia and algae having a lower sensitivity than fish. 

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