ASTM D6046 Standard Classification of Hydraulic Fluids for Environmental Impact
5. Basis of Classification
5.1 This classification consists of two groups of tests, one group addressing the environmental persistence of hydraulic fluids (Category P) and one group addressing acute ecotoxicity of hydraulic fluids (Category T). The ecotoxicity categories are further divided into two environmental compartments, aerobic soil (Ts) and aerobic fresh water (Tw). At this time categories for environmental persistence are limited to aerobic fresh water (Pw).
5.2 All testing shall use as its starting point the unused fully formulated hydraulic fluid.
5.3 The classification of hydraulic fluids for environmental persistence is defined by the hydraulic fluid's biodegradability as measured in tests for either ultimate or primary biodegradation. Pre-adaptation of inoculum for a period of up to two weeks is allowed for all categories. The classification system is given in Table 2.
5.3.1 Table 2 is divided into three parts. Part A, for hydraulic fluids with elemental analyses indicating a contents of less than 10 wt % oxygen, has separate requirements for tests which measure % theoretical CO2 and % theoretical O2. For these hydraulic fluids the different numerical results for the two different types of ultimate biodegradability tests are technically equivalent. Part B for hydraulic fluids with elemental analyses indicating a contents of 10 wt % or more oxygen has the same numerical result for both types of ultimate biodegradation test and these numerical results are also technically equivalent. The difference between hydraulic fluids containing little oxygen and fluids containing relatively abundant oxygen is related to the use of the oxygen present in the base stocks by the microorganisms. Further information is given in Appendix X1.
5.3.1.1 Oxygen content of hydraulic fluids is most commonly determined by difference, that is, by determining the other elemental components of the hydraulic fluid and subtracting that percentage from 100. For purposes of this classification determination of carbon, hydrogen, and nitrogen by Test ethod D5291 and subtraction of that total from 100 is acceptable. Direct determination of elemental oxygen by neutron activation is also acceptable.
5.3.1.2 Table 2 has been constructed assuming that 60 % of the carbon in the hydraulic fluid goes directly to CO2 during biodegradation and that the remaining carbon is converted to biomass.
5.3.2 Class Pw1 includes hydraulic fluids which would be expected to be the least persistent in the environment. It may be assumed that such a fluid would rapidly and extensively biodegrade in an aerobic aquatic environment which contains microbial life and the conditions necessary for it.
5.3.2.1 Although a minimum production of 60 % theoretical CO2 or greater up to but not including 100 % theoretical CO2 or consumption of the technically equivalent fraction of theoretical O2 leads to a strong implication that the hydraulic fluid will rapidly and extensively biodegrade, such a finding does not unequivocally rule out the possibility that the biodegradation produces recalcitrant metabolites not normally found in nature. Recalcitrant metabolites could constitute a persistent residue of the hydraulic fluid that may remain in the environment. It is also possible that a very small fraction of the original hydraulic fluid, perhaps an additive, could not be biodegraded and could persist in the environment.
5.3.3 Class Pw2 includes hydraulic fluids which would not be expected to persist in the environment in the long term. It may be assumed that these fluids would most likely be biodegraded eventually in an aerobic aquatic environment which contains microbial life and the conditions necessary for it.
5.3.3.1 As with category Pw1, incomplete biodegradation during the test time does not unequivocally define the extent to which the hydraulic fluid is fully and completely utilized, and so the inclusion of a hydraulic fluid in this class does not unequivocally rule out the possibility that a persistent residue of the hydraulic fluid may remain in the environment.
5.3.4 Class Pw3 includes hydraulic fluids which will not persist in the environment in an unchanged state. It may be assumed that either some or all components of the fluid will biodegrade to some extent, but not necessarily completely, in an aerobic aquatic environment which contains microbial life and the conditions necessary for it.
5.3.5 Class Pw-C includes hydraulic fluids which are not likely to persist in the environment in an unchanged state. This is inferred from results of the primary biodegradation test CEC L-33-A-934. Since primary biodegradation tests do not measure the extent to which the hydraulic fluid is fully and completely utilized and so no longer exists in the environment, inclusion of a hydraulic fluid in this class leaves open the possibility that a persistent residue of the hydraulic fluid may remain in the environment. Because this class is defined by the results of a primary biodegradation test, it is possible for a hydraulic fluid to belong to this class and to one of the other persistence classes.
5.3.6 Class Pw4 includes hydraulic fluids which exhibit low biodegradability and are expected to remain in an aerobic aquatic environment for relatively long periods of time. In the environment these fluids may or may not undergo biologically induced changes. Further testing, such as field studies, would be required to establish biodegradability of materials falling into this category. In the event that results for tests of both ultimate and primary biodegradability are available for a hydraulic fluid, the fluid will be assigned the designation Pw4 only if the criteria for that designation are met for both types of test.
5.3.7 To establish a designation it is necessary to run only one of the recommended methods.
5.3.8 In the event that the results of different tests for one hydraulic fluid are available, the highest result achieved among the Pw classes shall determine the classification. For example, if results for a hydraulic fluid based on a hydrocarbon in a test for theoretical CO 2(refer to Table 2, Part A for hydraulic fluids containing less than 10 weight % O2) gave 64 % in 28 days, giving a designation of Pw1, while the results from a test for theoretical O2 gave 62 % in 84 days, for a designation of Pw3, the classification will be Pw1 and not Pw3. That is, the tests are designed so that they are unlikely to find a material to be highly biodegradable if it is not. There is a much higher probability that a test will find a material to have a low biodegradability when in most natural environments it will biodegrade.
5.4 The classification of hydraulic fluids for acute ecotoxicity is given in Table 3. The ecotoxicity classification is further divided into two environmental compartments, aerobic soil, and aerobic fresh water.
5.4.1 Acute ecotoxicity in an aquatic environment shall be tested with at least three tests of acute toxicity, one test being on a plant, one test on a vertebrate, and one test on an invertebrate appropriate for the aquatic compartment.
5.4.2 Acute ecotoxicity in a terrestrial environment shall be tested in at least two tests of acute toxicity, one on an invertebrate and one on a plant. Tests on terrestrial vertebrates usually fall under the category of mammalian toxicity rather than ecotoxicity and so are not included in this classification.
5.4.3 The lowest numerical endpoint shall determine the classification of the hydraulic fluid. For example, if the LL50 for an aquatic vertebrate was 1150 wppm (Tw1) and the IL50 for algal growth was 800 wppm (Tw2), the rating would be Tw2.
5.4.4 If the hydraulic fluid contains materials regarded as carcinogenic (as per 29 CFR, part 1910) in an amount exceeding 0.1 wt %, the hydraulic fluid will not be eligible for the Tw1 or Ts1 designation. If ecotoxicity test results for the hydraulic fluid exceed 1000 wppm LL50, EL50, or IL50, the designation shall be Tw2 or Ts2 as appropriate.
5.5 Ecotoxicity testing of each fully formulated hydraulic fluid to be classified is preferable. However in the case where a hydraulic fluid is formulated at a viscosity grade intermediate to two tested fluids which are both in one designation, then that same designation may be used for the untested fluid provided the following conditions are met.
5.5.1 The change in viscosity grade is achieved by changing the proportions of two or more base stocks which are all present in both tested fluids. No new base stocks are introduced.
5.5.2 The same additives in both the same proportions and overall treat rate are used for all three fuids.
