Ecotoxicity of foaming agent conditioned soils on two terrestrial organisms

Commercial foaming products are used as lubricants to facilitate the excavation process in mechanized tunnelling by means of tunnel boring machines (TBMs). These foaming mixtures contain anionic surfactants (AS) as the main component and other additives, generally polymers, not always of a known chemical composition. Sodium lauryl ether sulphate (SLES) is one of the most used AS in foaming agents, in a concentration ranging from 10 to 50% of the overall commercial product. The possible re-use of the huge amount of soil debris produced during the excavation process as by-products (e.g. land covering) or its discharge as a waste depends on the residual concentration of AS in the soil. The first option has the undoubted advantage to lower the costs of disposal. However, concerns are present about the potential environmental risk related to the re-use of conditioned soil. In fact, even if anionic surfactants are generally considered biodegradable and not toxic, information on their biodegradation rates in soil as well as on the ecotoxicological effects of the commercial formulations of foaming products are quite scarce. Therefore an improve in knowledge of these aspects would be very relevant for the decision making processes of stakeholders. In the present work, we report some results regarding the biodegradation and ecotoxicological effects of several foaming agents. In particular, we performed two tests using terrestrial organisms such as the plant Lepidium sativum and the earthworm Eisenia foetida. The tests were conducted following the traditional OECD protocols, but using soils conditioned with foaming agents derived from tunnelling as substrate.