OECD GUIDELINES FOR THE TESTING OF CHEMICALS.docx

1、OECD GUIDELINES FOR THE TESTING OF CHEMICALSPROPOSAL FOR A NEW GUIDELINE Bioaccumulation in Sediment-dwelling Benthic Oligochaetes INTRODUCTIONSediment-ingesting endobenthic animals may be exposed to sediment bound substances (1). Among these sediment-ingesters, aquatic oligochaetes play an importan

2、t role in the bottoms of the aquatic systems. They live in the sediment and often represent the most abundant species especially in habitats with environmental conditions adverse to other animals. By bioturbation of the sediment and by serving as prey these animals can have a strong influence on the

3、 bioavailability of such substances to other organisms, e.g. benthivorous fish. In contrast to epibenthic organisms, endobenthic aquatic oligochaetes burrow in the sediment, and ingest sediment particles below the sediment surface. Because of that, these organisms are exposed to chemicals via many u

4、ptake routes including direct contact, ingestion of contaminated sediment particles, porewater and overlying water. Some species of benthic oligochaetes that are currently used in ecotoxicological testing are described in Annex 6.The parameters which characterise the bioaccumulation of a substance i

5、nclude first of all the bioaccumulation factor (BAF), the sediment uptake rate constant (ks) and the elimination rate constant (ke). Detailed definitions of these parameters are provided in Annex 1.To assess the bioaccumulation potential of chemicals in general, and to investigate the bioaccumulatio

6、n of substances which tend to partition into or onto the sediments, a compartment-specific test method is needed (1) (2) (3) (4).This Test Guideline is designed to assess bioaccumulation of sediment-associated chemicals in endobenthic oligochaete worms. The test substance is spiked into the sediment

7、. Using spiked sediment is intended to simulate a contaminated sediment.This guideline is based on existing sediment toxicity and bioaccumulation test methods (1) (4) (5) (7) (8) (9) (10). Other useful documents are: the discussions and results of an international workshop (12), and the outcome of a

8、n international ring test (62).This test applies to stable, neutral organic chemicals, which tend to associate with sediments. Bioaccumulation of sediment-associated, stable metallo-organic compounds can also be measured with this method (13). It is not applicable to metals and other trace elements

9、(12). PREREQUISITE AND INFORMATION ON TEST SUBSTANCEThere are only a few well established Quantitative Structure-Activity Relationships (QSAR) concerning bioaccumulation processes presently available (14). The most widely used relationship is the correlation between the bioaccumulation and bioconcen

10、tration of stable organic substances (expressed as log Kow; see Annex 1 for definition) and their lipophilicity, respectively, which has been developed for the description of a substance partitioning between water and fish. Correlations for the sediment compartment have also been established using t

11、his relationship (15) (16) (17) (18). The log Kow-log BCF correlation as a major QSAR may be helpful for a first preliminary estimation of the bioaccumulation potential of sediment-associated chemicals. However, the BAF may be influenced by lipid content of the test organism and the organic carbon c

12、ontent of the sediment. Therefore the Koc is a major determinant of the bioaccumulation of sediment-associated organic compounds.This test is applicable to: - stable, organic substances having log Kow values between 3.0 and 6.0 (5) (19); - superlipophilic substances that show a log Kow of more than

13、6.0 (5);- substances which belong to a class of organic substances known for their bioaccumulation potential in living organisms, e.g. surfactants or highly adsorptive substances Information on the test substance such as safety precautions, proper storage conditions and analytical methods should be

14、obtained before beginning the study. Guidance for testing substances with physical-chemical properties that make them difficult to test is provided in (21). Before carrying out a test for bioaccumulation with aquatic oligochaetes, the following information about the test compound should be known whe

15、n available:- common name, chemical name (preferably IUPAC name), structural formula, CAS registry number, purity;- solubility in water Guideline 105; (22);- octanol-water partition coefficient, Kow Guidelines 107, 117; (22);- sediment-water partition coefficient, expressed as Koc Guideline 121 (22)

16、;- hydrolysis Guideline 111; (22);- phototransformation in water (23);- vapour pressure Guideline 104; (22);- Henrys law constant;- ready biodegradability Guidelines 301 A to F; (22);- biodegradation in the aquatic environment (Guidelines 308 and 309; (22)- surface tension Guideline 115; (22);- crit

17、ical micelles concentration (24). Radiolabelled test substances can facilitate the analysis of water, sediment and biological samples, and may be used to determine whether metabolites identification and quantification should be made. The method described here was validated in an international ring t

18、est (62) for 14C-labelled compounds. If total radioactive residues are measured the bioaccumulation factor (BAF) is based on the parent compound including any retained metabolites. It is also possible to combine a metabolism study with a bioaccumulation study by analysis and quantification of the pe

19、rcentage of parent compound and its metabolites in samples taken at the end of the uptake phase or at the peak level of bioaccumulation. In any case, it is recommended that BAF calculation be based on the concentration of the parent compound in the organisms and not only on total radioactive residue

20、s.In addition to the properties of the test substance, other information required is the toxicity to the oligochaetes species to be used in the test, preferably an LC50 for the time necessary for the uptake phase. Preference should be given to toxicity values derived from long-term studies on sublet

21、hal endpoints. If such data are not available, an acute toxicity test under conditions identical with the bioaccumulation test conditions may provide useful information. An appropriate analytical method of known accuracy, precision, and sensitivity for the quantification of the substance in the test

22、 solutions, in the sediment, and in the biological material must be available, together with details of sample preparation and storage as well as material safety data sheets. Analytical detection limits of the test substance in water, sediment, and worm tissue should also be known. If a 14C-labelled

23、 test substance is used, the specific radioactivity (i.e. Bq mol-1) and the percentage of radioactivity associated with impurities must also be known. The specific radioactivity of the test compound should be as high as possible in order to detect test concentrations as low as possible (12).Informat

24、ion on characteristics of the sediment to be used (e.g. origin of sediment or its constituents, pH and ammonia concentration of the pore water (field sediments), organic carbon content (TOC), particle size distribution (percent sand, silt, and clay), and percent dry weight) should be available (7).P

25、RINCIPLE OF THE TESTThe test consists of two phases; the uptake (exposure) phase and the elimination (post-exposure) phase. During the uptake phase, worms are exposed to sediment spiked with the test substance, topped with reconstituted water and equilibrated as appropriate (12). Groups of control w

26、orms are held under identical conditions without the test substance. For the elimination phase the worms are transferred to a sediment-water-system free of test substance. An elimination phase is necessary to gain information on the rate at which the test substance is excreted by the test organisms

27、(19) (20). An elimination phase is always required unless uptake of the test substance during the exposure phase has been insignificant (e.g. there is no statistical difference between the concentration of the test substance in test and control worms). If a steady state has not been reached during t

28、he uptake phase, determination of the kinetics BAFk, uptake and elimination rate constant(s) may be done using the results of the elimination phase. Change of the concentration of the test substance in/on the worms is monitored throughout both phases of the test. During the uptake phase, measurement

29、s are made until BAF has reached a plateau or steady state. By default, the duration of the uptake phase should be 28 days. Practical experience has shown that a 12 to 14-day uptake phase is sufficient for several stable, neutral organic substances to reach steady-state (7) (9) (10). However, if the

30、 steady state is not reached within 28 d, the elimination phase is started by transferring exposed oligochaetes to vessels containing the same medium without the test substance. The elimination phase is terminated when either the 10% level of steady state concentration or of the concentration measur

31、ed in the worms on day 28 of the uptake phase is reached, or after a maximum duration of 10 d. The residue level in the worms at the end of the elimination phase is reported as endpoint, e.g. as Non-eliminated residues (NER). The bioaccumulation factor (BAFss) is calculated preferably both as the ra

32、tio of concentration in worms (Ca) and in the sediment (Cs) at apparent steady state, and as a kinetic bioaccumulation factor, BAFK as the ratio of the rate constant of uptake from sediment (ks) and the elimination rate constant (ke) assuming first-order kinetics. If a steady state is not reached within 28 days, calculate BAFK from the uptake rate and elimination rate constant(s). For calculation see Annex 2. If first-order kinetics are not applicable, more complex models should be employed (Annex 2 and reference (26). If a steady state is not achieved within 28 days, the uptake phase