Final acute value

Final acute values for freshwater and saltwater organisms were determined to be 80.01 and 140.8 pg/L, respectively. Acute toxicity values determined from individual toxicity tests for freshwater and saltwater organisms ranged from 120.0 to 2,045 and 160 to 16,440 pg/L, respectively (U.S. EPA, 1993). 

Acute toxicity values (LC50) for freshwater organisms ranged from 55.7pgH for the amphipod Hyalella azteca) to 774 pgH for the snail Phy-sella virgata). No relationships have been demonstrated between water quality characteristics (such as hardness and pH) and toxicity. The freshwater final acute value (FAV) for NP is 55.7pgl which is equal to the LC50 for the most sensitive tested... 

Criterion maximum concentration The 1-hr average concentration of a toxicant not to be exceeded more than once every 3 yr and defined by the EPA to be half the final acute value. 

Final acute value The concentration of a toxic substance expected to equal or exceed the 96-hr TLm of 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. 

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... 

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. 

The final acute/chronic ratio is considered to be a measure of the ratio of the concentration of the toxic substance associated with acutely toxic effects to the concentration associated with chronic toxicity effects. According to the methodology recommended by the EPA (1985a), the final acute/chronic ratio may be calculated in one of four ways. First, if there is no major trend apparent among the acute/chronic ratios for the different species and the species mean acute/chronic ratios lie within a factor of 10 for a number of species, the final acute/chronic ratio is the geometric mean of all the species acute/chronic ratios available for both fi eshwater and saltwater species. Second, if the species mean acute/chronic ratios seem to be correlated with the species mean acute values, the final... 

If tlie pollutant causes iui acute non carcinogenic risk, tlie inaximuin one hour concentration is used for C, and tlie acute reference exposure limit is used for tlie REL. Likewise, if tlie pollutant causes a clironic non carcinogenic risk, tlie one year average concentration is used, as is tlie clironic reference exposure limit. In tliis procedure, a Iiazard index is calculated for each pollutant separately, and tlien tlie indices are summed for each toxicological endpoint (i.e., tlie respiratory system, tlie central nervous system, etc.). Finally, tlie total hazard index is tlien compared to a value wliich is considered significant. 

This analysis takes the final observation for each patient and uses it as that patient s endpoint in the analysis. For example, in a 12 month trial in acute schizophrenia, a patient who withdraws at month 7 due to side effects will have their month 7 value included in the analysis of the data. 

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