Overview on the Results of the Ring Test

Abstract

The assessment of waste as hazardous or non-hazardous, according to the European Waste List, includes ecotoxicological characterization. Despite being made into national law by the Waste List Ordinance 2001, no recommendations on the methodology have been provided to cover the hazard criterion (H14 “ecotoxic”), which was taken from the legislation on dangerous substances. Based on the recommendations of CEN guideline 14735 (2005), an international ring test was organized by the German Environment Agency (UBA) with the help of the Federal Institute for Materials Research and Testing (BAM), FH Giessen-Friedberg and ECT Oekotoxikologie GmbH. Sixty laboratories from 15 countries participated in the ring test. It was performed with three representative waste types: ash from an incineration plant contaminated mainly with heavy metals (INC), soil containing high concentrations of organic contaminants (PAHs) (SOI) and preserved wood waste contaminated with copper and other heavy metals (WOO). Samples were prepared (inter alia dried, sieved and homogenized) and distributed by BAM. Parallel to the biological testing, the eluates and solid samples were chemically characterized. The basic test battery used in the ring test consisted of three aquatic (Algae test, Daphnia acute test and Microtox test) and two terrestrial (earthworm acute and plant test with two species (oat, rape)) tests. In addition, data were submitted for ten other tests (five aquatic (including a genotoxicity test) and five terrestrial). Almost all tests were performed according to ISO guidelines, providing EC₅₀ values as measurement of toxicity. Data evaluation was done following recent recommendations made by ISO (2002) and Environment Canada (2005).

In addition to data from several reference tests, 634 data sets were produced from the basic test battery, 196 data sets from additional test battery and, in parallel, 218 data sets with the respective reference substances. Only a few data sets were not acceptable (e.g. due to lack of reference data) and even fewer results were identified as statistical or biological outliers. For example, in the case of the basic test battery, the acceptance rate varied between 74.1 (Algae test) and 92.6% (Daphnia test). There were no methodological problems, but further guidance on moisture determination in the terrestrial tests, as well as details concerning reference testing and data evaluation for several tests, is needed. However, changes in the procedures described by CEN 14735 (2005) for the preparation of eluates may have caused some of the variability observed in the aquatic tests.

Independently which test system is considered, SOI always had the lowest effects and WOO was the most toxic, while the EC₅₀ values of INC showed an intermediate toxicity. Among the aquatic tests, daphnids and one algal species were the most sensitive ones, while plants were always more sensitive than earthworms in the terrestrial tests. A comparison of the ring test results with literature data published so far revealed good agreement, but the high sensitivity of daphnids, as well as the low sensitivity of the luminesecent bacteria, was not expected, because of the small number of data reported in the literature. Taking into account the differences between chemical/physicochemical and ecotoxicological ring tests, this variation is considered acceptable.

Based on the results from the additional tests, proposals for the modification of the existing basic test could be made. Most importantly, it was proposed that the acute earthworm test should be replaced by a more sensitive soil invertebrate test, in particular those with short durations (e.g. the Earthworm avoidance test or the Arthrobacter test, because of their combination of practicability and sensitivity). Available information indicates that besides “traditional” test versions with daphnids and algae, miniaturized microplate methods can be used. The same experience can also be used to find test methods for wastes which cannot be tested with the basic tests (e.g. the Lemna test for turbid eluates which cannot be tested in the Algae test). Finally, the ring test results also support the proposals made in the CEN guideline 14735 (2005) concerning the performance of such tests.

Further work, performed in parallel to the ring test, improves waste testing considerably. For example, special consideration should be given to the preparation of the terrestrial control and dilution medium (OECD artificial soil), as the variability of its properties may also have contributed to the overall variability of test results. Independent of the objectives of the ring test, the data collected can be used in combination with a detailed characterization of the eluates for the modeling of the bioavailable fraction of the respective contaminant, thus allowing the ecotoxicological effects observed in the tests to be understood.

In any case, more experience with different types of waste materials is necessary for all ecotoxicological test systems discussed so far, to define the range of materials which can successfully be tested. The same information is also necessary for the definition of limit values as well as for the identification of the most efficient testing strategy (e.g. the application of extended laboratory tests instead of full dose-response tests). In this context the collection of all relevant data as well as legal requirements in a data-base, together with the appropriate software like the H14-Navigator, is recommended, to improve data evaluation.

In line with recommendations made in the literature, a combination of the results of a battery of biological tests and chemical residue analysis is needed for an ecotoxicological characterization of wastes. The results and experiences from the ring test should be transferred to a harmonized approach for the implementation of the hazard criterion H14, as part of a future amendment of the European Waste List. In addition, basically the same approach - but with modifications of the test strategy and also test methods - can be used for an environmental risk assessment (ERA) of wastes. ERA is a very important prerequisite for the management of wastes, for example in re-use scenarios in which wastes come in direct contact with the environment.