Environmental fate studies

This Test Guideline describes an experimental method using HPLC for the estimation of the adsorption coefficient (K_oc) in soil and in sewage sludge. The adsorption coefficient is defined as the ratio between the concentration of the substance in the soil/sludge and the concentration of the substance in the aqueous phase at adsorption equilibrium. The test item is injected in the column packed with cyanopropyl solid phase containing lipophilic and polar moieties. As a result of partitioning between mobile and stationary phases the test item is retarded. The retention time is determined in duplicate.

The purpose of the test is to provide a rapid screening method to assess the effects of substances on the microorganisms of the activated sludge of the biological (aerobic) stage of waste-water treatment plants. The results of the test may also serve as an indicator of suitable non-inhibitory concentrations of test item to be used in biodegradability tests (for example OECD TG 301 series, TG 310, TG 302 series and TG 303). In this case, the test can be performed as a screening test, similar to a range-finding or limit test, considering the overall respiration only. However, this information should be taken with care for ready biodegradability tests (OECD TG 301 series and TG 310) for which the inoculum concentration is significantly lower than the one used in this Test Guideline. Indeed, an absence of inhibition in this respiration test does not automatically result in non-inhibitory conditions in the ready biodegradability test of the TG 301 series or TG 310.

A test item is exposed to an inoculum in a closed environment as part of the OECD 301 aerobic biodegradation test, which analyses the substance's biodegradation by parameters such as DOC, BOD, or CO₂ measurements. This set of test identifies substances that do not require additional testing if they pass the OECD 301 test. A test item considered readily biodegradable if it achieves 60% of chemical breakdown within 28 day period according to OECD 301 D. When a sample is able to pass the test, it is considered that it has the ability to biodegrade rapidly and thoroughly in the environment, and therefore known to be readily biodegradable. Hence, more research is typically not needed to determine a substance's biodegradability, toxicity, or other environmental impacts.

The 301 set of test guidelines are screening tests and if a test item doesn't pass the tests, it doesn't always follow that it can't degrade in more natural environmental settings. Higher level exams like OECD 302 should be taken as an alternative. A mixture containing the test item, mineral nutrients and a relatively large amount of activated sludge in aqueous medium is agitated and aerated at 20-25°C in the dark or in diffuse light for up to 28 days. The degradation is checked by measuring the Chemical Oxygen Demand (COD) or Dissolved Organic Carbon (DOC) of control and test item. The test is considered valid if the procedural control shows the removal of the reference compound by at least 70% within 14 days and if the removal of DOC (or COD) in the test suspension took place relatively gradually over days or weeks, since this indicates biodegradation.

The OECD 305 determines the bioaccumulation of test item in fish after getting exposed through aqueous exposure or dietary exposure. Research on aquatic organisms has revealed a significant beneficial correlation between an organism's lipid content and the concentration of a chemical that accumulates in it.  This test can be performed either in flow though condition or semi static state. Both the exposure involve two phases; first is uptake phase and second is depuration phase. In uptake phase, fish are exposed to test substance for 28 days after that fish are transferred to untreated water for depuration phase (28 days).  After completion of both the phases bioaccumulation rate is measured. The bioconcentration factor (BCF), the uptake rate constant (ks), and the elimination rate constant (ke) all have an important role in determining how much of the sample is bioaccumulated.  

Aerobic mineralisation in surface water is a biodegradation simulation test that assesses the mineralisation and biodegradation of a test item at low concentrations in aerobic natural water in the form of kinetic rate expressions. For up to 60 days, tests are run in batches to simulate suspended solids and suspended silt, with regular checks for degradation. Oxygen level and pH are also measured. The test substance's degradation will be monitored for both the parent substance's possible (known) transformation products. For the test item, the rate of degradation, the mass balancing, and the pattern of the transformation product will be determined. Incubation in surface water (the "pelagic test") will be carried out aerobically with agitation (shaking) at a temperature of 20°C in the dark. In order to collect CO₂ and other volatiles in various traps made of various solutions, a moderate stream of air will be employed as the carrier gas. The test will be conducted using two concentrations of the test material that varied by a factor of 5 to 10. Two concentrations chosen will be <10 μg/L and >100 μg/L respectively. The test duration will be 60 days. The selection of time intervals will allow for the identification of the test item's pattern of decline and any potential transformation products.