TEST ÉCOTOXICOLOGIQUE LAITUE LACTUCA SATIVA (L.)

Article soumis à CRBiol 

“Treated wastewater phytotoxicity assessment using Lactuca sativa : Focus on germination and root elongation test parameters”. Authors : Anne Priac, Pierre-Marie Badot, Grégorio Crini. Abstract : Sensitive and simple ecotoxicological bioassays like seed germination and root elongation tests are commonly used to evaluate phytotoxicity of waste and industrial discharge waters. Although the tests are performed following national and international standards, various parameters such as the number of seeds per dish, test duration or type of support used remain variable. To be able to make a correct comparison of results from different studies, it is crucial to know which parameter(s) could affect ecotoxicological diagnosis. We tested four different control waters and three seed densities. No significant differences on either germination rate or root elongation endpoints were shown. Nevertheless, we found that the four lettuce cultivars (Appia, Batavia dorée de printemps, Grosse Blonde Paresseuse and Kinemontepas), showed significantly different responses when watered with the same and different metal-loaded industrial discharge water. From the comparison, it is clear that a differential sensitivity scale occurs among not just species but cultivars.

Introduction

Surface treatment (ST) is a very important industrial sector in Europe and in France, Franche-Comté is especially concerned. ST is well known to be one of the largest consumers of chemicals (toxic metals known to be harmful to humans and to the environment in particular) and water and to generate large amounts of toxic waste water with a complex composition [1]. Despite the efforts made to clean up their polycontaminated effluents, most commonly by physicochemical treatment [2], industry and scientists are confronted with a great challenge: to remove the entire load of organic and inorganic pollutants to assess their ecotoxicological effects and hence move towards zero pollution discharge [3,4]. While pollutant mixtures present in discharge water after treatment are relatively easy to characterize chemically, assessing their impact on the environment is usually difficult [2]: over the past few decades, ecotoxicological methods have been developed to complete chemical analysis [5]. Bioassays are widely carried out following national and international recommendations. Some very different organisms are commonly used in ecotoxicological bio-monitoring: primary producers (algae i.e.: Pseudokirchneriella subcapitata [6]), primary consumers (aquatic invertebrates i.e.: Daphnia magna, Gammarus pulex [7]) or secondary consumers (aquatic vertebrates i.e.: Gambusia holbrooki [8]). Less frequently used in comparison with faunal tests [9], toxicity studies using higher plants have however increased in recent years [11-12]. Ratsch [13] first concluded that the inhibition of root elongation is a valid and sensitive indicator of environmental toxicity. Several articles [10, 14-20] have since shown that phytotoxicity tests like seed germination rate (GR) and root elongation (RE) tests present many advantages as summarized in Table II.1. These bioassays are simple, inexpensive and only require a relatively small amount of sample. Moreover, the seeds remain usable for a long time. The most common plant species recommended by, among others, the US Environmental Protection Agency [21], the US Food and Drug Administration [22] and the Organization for Economic Cooperation and Development [23] are cucumber Cucumis sativus, lettuce Lactuca sativa L., radish Raphanus spp L., red clover Trifolium pratense L. and wheat Triticum aestivum. Previous studies [20, 24] compared some of these species and recommended L. sativa as a bioindicator to determine the toxicity of soil and water samples.

 Industrial discharge water

During this study, discharge waters were once collected in 3 different surface treatment companies (denoted Co1, Co2 and Co3) in the Franche-Comté region. This industrial sector has to have a decontamination station before discharging effluent in the environment. Effluent samples were collected at the outlet of the decontamination station of each company. The main activities of each company and the related major environmental concerns are reported in Table II.3. The table also shows the concentration threshold in discharge for key pollutants. The effluents are average samples, characteristic of day’s activity. Each treated water sample was tested following the same concentration range: 25, 50, 75 and 100%. All dilutions were prepared in Reverse Osmosis Water (ROW). Table II.3. Main environmental issues encountered by the two surface treatment companies and the regulatory values (in mg L1 ) for different pollutants contained in the water discharges (French law of 5th September 2006).