User Guide to Thresholds and Classification - Environmental ...

362User Guide for Thresholds and ClassificationsThe OPPTS 835.5270 screening test concerns indirect photolysis of chemicals in waters that contain humicsubstances. The principle of the test is that in natural waters exposed to natural sunlight a measuredphototransformation rate will include both direct and indirect phototransformation, whereas only directphototransformation will take place in pure water. Therefore, the difference between the directphotodegradation rate in pure water and the total photodegradation in natural water is the sum of indirectphotolysis and secondary photodegradation. In the practical application of the test, commercial humicsubstances are used to make up a synthetic humic water, which mimics a natural water. It should be notedthat the indirect phototransformation rate determined is only valid for the season and latitude for which it isdetermined and it is not possible to transfer the results to other latitudes and seasons.Biotic degradabilityOnly a brief overview of the test methods is given below. For more information, consult the comprehensivepaper Detailed Review Paper on Biodegradability Testing (OECD, 1995).Ready biodegradabilityStandard tests for determination of the ready biodegradability of organic substances aredeveloped by a number of organisations including OECD (OECD Test Guidelines 301A-F), European Union(EU) (C.4 tests), OPPTS (835.3110) and International Organization for Standardization (ISO) (9408, 9439,10707).The ready biodegradability tests are stringent tests, which provide limited opportunity for biodegradation andacclimatisation to occur. The basic test conditions ensuring these specifications are:high concentration of test substance (2–100 mg/L);the test substance is the sole carbon and energy source;low to medium concentration of inoculum (104–108 cells/mL);no pre-adaptation of inoculum is allowed;28-day test period with a 10-days time window (except for the MITI I method (OECD Test Guideline301C)) for degradation to take place;test temperature < 25°C; andpass levels of 70% (DOC removal) or 60% (O2 demand or CO2 evolution) demonstrating completemineralisation (as the remaining carbon of the test substance is assumed to be built into the growingbiomass).It is assumed that a positive result in one of the ready biodegradability tests demonstrates that the substancewill degrade rapidly in the environment (OECD 301 Test Guidelines).Also the traditional BOD5 tests (for example, the EU C.5 test) may demonstrate whether a substance isreadily biodegradable. In this test, the relative biochemical oxygen demand in a period of 5 days is comparedto the theoretical oxygen demand (ThOD) or, when this is not available, the chemical oxygen demand(COD). The test is completed within 5 days and consequently, the pass level defined in the proposed hazardclassification criteria at 50% is lower than in the ready biodegradability tests.January 2012 EPA0109