© by PSP Volume 21 – No 4. 2012 Fresenius Environmental Bulletin 844 SINGLE AND JOINT EFFECTS OF PERCHLORATES TO DAPHNIA MAGNA: ADDITIVITY AND INTERACTION PATTERNS Susana Loureiro 1, *, Tayvia L. Meyer 1 , Abel L. G. Ferreira 1 , Mónica J. B. Amorim 1 and Amadeu M. V. M. Soares 1 1 Department of Biology & CESAM, University of Aveiro, 3810-193 Aveiro, Portugal. ABSTRACT Frequent cases of soil and water contamination by perchlorates, and consequent toxicity to plants, animals and humans have drawn attention worldwide. Anthropogenic actions are the main cause for this pollution. Due to high levels of oxidation, perchlorates are commonly used to produce solid propellants for rockets and missiles, fire- works, and air bag inflators and also as bleach in paper industry. In this work we assessed the effects of ammo- nium and sodium perchlorates singly and in mixture to Daphnia magna by studying the endpoints: immobiliza- tion, reproduction, growth and feeding activities. At short time exposures characterized with immobili- zation and feeding parameters, ammonium perchlorate was 10 times more toxic to D. magna than sodium per- chlorate. On the other hand, toxicity was similar when a long-term exposure with reproduction parameter was carried out. The mixture toxicity approach also showed that sodium perchlorate was ruled for synergistic patterns when dominant in the short-term exposure tests. When evaluating the reproductive effort by using the number of neonates, the concentration addition model was the best fit. This study shows that the different properties of two chemicals, highlighting the possible synergy that can occur when chemicals are present in mixtures, will be of high re- levance to improve Cumulative Risks assessment proce- dures. KEYWORDS: Perchlorates; mixture; synergism, acute toxicity; chronic toxicity; Daphnia magna. 1. INTRODUCTION Mixture toxicity and multiple stresses is one of the considerable areas where risk assessment of chemicals should and has been considerably improved. The shift from a single-compound to a cumulative approach has consequences for the assessment of exposure, effects and * Corresponding author risks. In addition, new techniques for chemical detection lead to the acknowledgement of new threats to the envi- ronment and human health [1, 2]. Perchlorates (ClO -4 ) have become of environmental concern after being found in several water supplies in 1997, in the United States of America [2]. They had been detected in groundwater, drinking water, soils and vegetation and were found in places with routinely use of explosives, solid propellants, rockets, missiles and fireworks, wastewater and industrial discharge or urban runoff, and are known to be also re- leased to the environment by research laboratories and fertilizers [1-3]. The Massachusetts Public Water Supplies detected in 2005 perchlorate concentrations ranging from 783 – 1300 µg/L, in a condominium nearby a bedrock aquifer, possibly due to blasting activities (http://www. mass.gov/dep/cleanup/sites/percsour.pdf). In Europe, little information is available on perchlorates in the environ- ment, however perchlorate concentrations of 0.8 mg/L were recorded in soil leachates collected from an oak- hornbeam forest, in northeast Vernun (France, in addition to heavy metals and chlorates (71 mg/L) [4]. Although some data about the ecotoxicological effects of perchlorates was reported for the zebra fish (Danio rerio) [5], the frog Rana sphenocephala [6], the fish Gos- terosteus aculeatus [7], or the molly fish Poecilia sphenops [8], effects on invertebrates have not been widely studied. The survival and reproductive success of earthworms [9] and the acute and chronic toxicity of the larval mosquito Culex quinquefasciatus [10] are examples of what have been described. Perchlorate salts often appear associated with other (per)chlorates or chemicals and therefore their joint toxic- ity is a key factor to be studied in addition to single chemical toxicity. The aim of this study was to evaluate the combined effects of ammonium and sodium perchlorates using Daphnia magna as a model organism. To achieve this goal, a first approach to detect toxicity patterns of their single toxicity was carried out. This information will be used as crucial foundations for the combined experiments, since prediction and modelling of mixture toxicity is based on single toxicities.