Chronic value

The Swiss law for water protection does not indicate a concentration hmit for aluminium in surface waters. Therefore, in order to better assess the measured aluminium concentrations, we compared them with the concentration limits existing in the US. The chronic US National Ambient Water Quality Criteria [19] for total aluminium at a pH of 6.5-9 is 87 pg 1, indicating that the average value over 4 days should not exceed this value more than once every 3 years. However, since aluminium seems to be more toxic at low pH s the result is that in acidic waters the acceptable chronic value of total aluminium may be even lower. We conclude that aluminium concentrations in our three most acid lakes are probably high enough to cause toxic effects on organisms. 

Dourson et al. (1996) referred to a number of examinations of subchronic-to chronic NOAEL ratios, which showed that the average difference between subchronic and chronic values was only 2-3. Based on these examinations as well as on the analysis by Lewis (1993) and unpubhshed work in US-EPA, the authors concluded that the routine use of a 10-fold default factor for this area of uncertainty should be examined closely. They noted that short-term (2 weeks) and subchronic (90 days) NOAELs are often available and can give an indication of the possible differences in the subchronic NOAEL and the expected chronic NOAEL. When such data are not available, a 10-fold UF may not be unreasonable, but should be considered as a loose upper-bound estimate to the overall uncertainty. 

Pesticide LC50 (Pg/L) Acute Toxicity Chronic Value ( xg/L) ACR Chronic Toxicity... 

Snell, T.W. (2000) The distribution of endpoint chronic value, for freshwater rotifer, in G. Persoone, C. Janssen and W.M. De Coen (eds.), New Microbiotests for Routine Toxicity Screening and Biomonitoring, Kluwer Academic/Plenum Publishers, New York, pp. 185-190. 

The ACRs are an established method to extrapolate to chronic values from acute data. 

QSARs for the prediction of toxicity to aquatic organisms, including fish, invertebrates and algae, are relatively well developed for a broad range of chemical classes. More than 100 SARs for 55 chemical classes are available in a free, downloadable model called ECOSAR from the EPA website, based on test data and assumptions from test data. Aquatic toxicity endpoints include reproduction, growth and mortality, such as acute toxicity to fish, invertebrates, and algae. The PBT Profiler also estimates chronic toxicity to fish by means of the ECOSAR model it compares the fish chronic value to maximum water solubility, in order to estimate potential for aquatic risk. 

Talmage et al. [4] analyzed an extensive TNT toxicity database and derived freshwater final acute and chronic values (FAV and FCV, respectively) of 4.99 and 0.410 pmoles E and the respective criterion maximum concentration (CMC) of 2.50 pmoles E that is, half the FAV. The lowest chronic effect value for fish, of 0.176 pmoles E, was suggested as a better screening benchmark than the calculated FCV until a sufficient chronic toxicity database becomes available [4], All these values are above the LOEC from nine-month life-cycle tests with fathead minnows, of 0.06 pmoles L 1 [76] (Table 4.2), suggesting that the proposed chronic values need to be revised for adequate long-term protection of aquatic life. 

Proposed interim TNT WQC for the protection of marine life were 0.376 and 0.125 pmoles L 1 for acute and chronic values, respectively [15], These criteria are expected to be protective of marine life, based on the sensitivity of marine and estuarine species to TNT given in the present review (Table 4.2). 

Final and Interim Acute and Chronic Values Derived as Water Quality Criteria (pmoles L 1) for the Protection of Aquatic Life... 

Data available in the scientific literature were not sufficient for the calculation of Tier I acute or chronic WQC with other energetic compounds and their transformation products. Tier II secondary freshwater acute and chronic values (SAV and SCV, respectively) were derived by Talmage et al. [4] for TNB, 1,3-DNB, 3,5-DNA, 2-A-4,6-DNT, HMX, and RDX, by dividing the lowest genus mean acute value (GMAV) by the secondary acute factor (SAF Table 4.7). 

Chronic values for 16% reproductive impairment were from Biesinger and Christensen (72). 

To highlight a chemical that may be chronically toxic to fish, the PBT profiler uses the following criteria Fish ChV (Chronic Value) > 10 mg/1 (low concern). Fish ChV = 0.1 - 10 mg/1 (moderate concern) and Fish ChV < 0.1 mg/1 (high concern). 

Criterion continuous concentration The 4-day average concentration of a toxicant not to be exceeded more than once every 3 yr and defined by the EPA to be the minimum of the final chronic value and the final plant value. 

Final chronic value The concentration of a toxic substance expected to exert a chronic stress on no more than 5% of the genera in an aquatic ecosystem. 

If data on a sufficient number and diversity of organisms are available, a final chronic value for a particular toxicant may be calculated in the same way that final acute values are determined. In practice, however, there are seldom sufficient data to allow a direct graphical estimation of the toxicant concentration that would exert a chronic stress on no more than 5% of the species in the system. In such cases an acute toxicity standard is established on the basis of an adequate amount of short-term toxicity tests, and an average acute/chronic toxicity ratio is then calculated on the basis of a smaller amount of information. The rationale for this procedure is that for a given pollutant the acute/chronic ratio is likely to be more constant between species than is the chronic or sublethal stress level itself Hence less information is required to estimate the acute/chronic ratio. The chronic toxicity standard is established by dividing the acute toxicity standard by the so-called final acute/chronic ratio. The EPA considers this procedure acceptable if acute/chronic ratios are available for at least three species and (a) at least one of the species is a fish, (b) at least one is an invertebrate, and (c) at least one is an acutely sensitive fi eshwater species or saltwater species when the ratio is being used to establish freshwater or marine criteria, respectively. 

An example of the calculation of a final acute/chronic ratio is shown in Table V for the pesticide dieldrin. Chronic values for this pesticide were available for only four species in 1980 when the guidelines for dieldrin were established (EPA, 1980a), and therefore it was necessary to use acute/chronic ratios to estabhsh the final chronic value. Acute toxicity values were available in only three of the four cases where chronic effects were studied, but the three species satisfied the criteria for calculating acute/chronic ratios in both freshwater and salt water. Since the acute/chronic ratios for the three species differed by less than a factor of 2, it was appropriate to calculate the final acute/chronic ratio for dieldrin by taking the geometric mean of the three ratios, which is [(11)(9.1)(6.2)] / = 8.5. Final acute values for dieldrin in freshwater (EPA, 1996b) and salt water are 0.48 and 0.71 ppb, respectively. Hence the final chronic values for dieldrininfreshwaterand saltwater areO.48/8.5 = 0.056 ppb and 0.71/8.5 = 0.084 ppb, respectively. 

Species Acute value (ppb) Chronic value (ppb) Ratio... 

Final acute value Final chronic value Final plant value Criterion maximum concentration Criterion continuous concentration... 

Under the present system (EPA, 1996b), the two numbers in the criterion are calculated from the final acute value, the final chronic value, and the final plant value. The three values for dieldrin in freshwater and salt water are shown in Table VII. The criterion maximum concentration is equated to half the final acute value. Division by 2 in this case to some extent corrects for the fact that much of the acute toxicity information is based on observations of lethal effects, whereas the real concern is protection of organisms fi om sublethal stresses. The criterion continuous concentration is the smaller of the final chronic value and the final plant value. 

An analogous equation for the final chronic value may be calculated by simply dividing the equation for the final acute value by the final acute/chronic ratio. However, if there is evidence that there is a difference in the functional dependence of chronic toxicity and acute toxicity on water quality characteristics such as temperature and hardness, then the final chronic equation may be determined independently of the final acute equation. In the case of cadmium, for example, chronic toxicity appears to be less sensitive to water hardness than acute toxicity appears to be, thus a final fi eshwater chronic equation was developed solely from chronic toxicity studies performed with 16 fi eshwater species. The final chronic equation for dissolved cadmium in fi eshwater is... 

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