Background, aim, and scope: The purpose of this study was to compare the suitability of different phytotoxicity testing procedures for the evaluation of toxicity associated with both soil contamination and solid wastes, both of which can be of environmental risk to plants. Ten different representative types of contaminated soils and solid waste samples were chosen from the Czech Republic.
Materials and methods: Both solid-phase and aquatic toxicity testing procedures on mono- and dicotyledonous plants were performed using Lactuca sativa L., Sinapis alba L., Hordeum vulgare L., Triticum aestivum L., Lemna minor L., and the chlorococcal algae Desmodesmus subspicatus (syn. Scenedesmus subspicatus), strain BRINKMANN: 1953/SAG 86.81. An innovative classification scheme, using the intensity of toxic effects upon the plants, is presented in the study. Detailed chemical characterizations of both solid samples and their aquatic elutriates were carried out, using the appropriate ISO guidelines. In the solid samples, all the congeners of polychlorinated biphenyls were analyzed, together with 16 U.S. EPA polyaromatic hydrocarbons, the aggregate of C10-C40 hydrocarbons, total organic carbon, extractable organic halogens, as well as the majority of the environmentally toxic metals. In the aquatic elutriates, parameters analyzed were pH, conductivity, dissolved organic content, phenol index, main anions, and the majority of the environmentally relevant metals.
Results: Eight out of ten samples tested expressed phytotoxic properties on tested organisms. Only three of the samples were toxic to both aquatic and terrestrial organisms in the tests. This demonstrates how different substances present in different samples can express different types of toxic effects, resulting in the illogical substituting terrestrial bioassays with aquatic ones.
Discussion: Based upon our experience, we propose the following battery of bioassays for use in the characterization of toxic properties of solid wastes and contaminated soils: Aquatic ecosystems were tested by the algae D. subspicatus and plant L. minor; and the terrestrial ecosystems were tested by the dicotyledonous L. sativa and monocotyledonous H. vulgare. This proposed new battery of bioassays for the detection of phytotoxicity of both solid wastes and contaminated soils has higher sensitivity (as well as greater ecological relevance) compared to the battery of bioassays currently used in the Czech Republic.
Conclusions: The tests currently used for regulatory purposes in the Czech Republic are phytotoxicity tests of elutriates, using S. alba and D. subspicatus, which have been found insufficiently sensitive to the range of different pollutants present in contaminated soils and/or solid wastes. If only aquatic bioassays are used for the toxicity testing, it is possible that the toxic effects of substances (poorly or totally) insoluble in water might be underestimated. The new proposed system of toxicity classification has proven to be both practical and sensitive.
Recommendations and perspectives: This recommended alternative battery of phytotoxicity tests includes both aquatic tests of waste elutriates (with the algae D. subspicatus along with the aquatic plant L. minor), in addition to tests of the terrestrial solid samples (with the dicotyledonous L. sativa and the monocotyledonous H. vulgare). This battery of bioassays is sufficiently sensitive, representing a majority of types of aquatic and terrestrial plants.