Rolf Altenburger

pH-Dependent sorption, bioconcentration and algal toxicity of sulfonylurea herbicides

Abstract Uptake and toxicity of four sulfonylurea herbicides (metsulfuron-methyl, chlorsulfuron, triasulfuron and tribenuron-methyl) to the freshwater microalga Chlorella fusca have been investigated under different pH regimes. Toxicity parameters were inhibition of (a) cell volume growth and (b) reproduction of synchronized cell populations, cultivated under photoautotrophic conditions. At pH 6.5, EC50 values ranged from 3.2 (metsulfuron-methyl) to 0.3 μmol/l (tribenuron-methyl) for the inhibition of cell volume growth, and from 2.2 to 0.2 μmol/l for the inhibition of cell reproduction. By lowering the pH of the growth medium to 5.0, the toxicity of chlorsulfuron was enhanced 25-fold, as indicated by an EC50 value of 44.0 nmol/l for the inhibition of reproduction. The bioconcentration of the four sulfonylureas in Chlorella did not exceed a factor of 9 at pH 6.0, but was significantly increased at pH 5.0, with a maximum value of 53 for chlorsulfuron. These results suggest that the sulfonylureas penetrate the algal cell membranes primarily in their undissociated form and accumulate by an ion trapping mechanism.

Algal toxicity of binary combinations of pesticides

Pollution of surface waters is rarely a matter of a single toxicant but aquatic organisms are typically exposed to numerous chemicals simultaneously or in sequence. Consequently, hazard assessment in aquatic toxicology cannot be restricted to considerations on individual compounds. Thereby the question arises whether there are rational approaches for a calculation of the toxicities of mixtures from the concentration response relationships of their components. This paper deals with the predictive value of concentration addition, a concept used for the analysis of combination effects (see Boedeker et al. 1992 for a review). It is given by the formula: Cl/ECx I + C2/ECx 2 = 1

Combined effects of toxicants: the need and soundness of assessment approaches in ecotoxicology

Abstract For the assessment of combined effects of toxicants mainly two competing concepts, concentration addition and response multiplication (independent action), are available. Concentration addition bears most experimental evidence and has therefore been recommended as a leading principle to calculate mixture toxicity. In this paper we compare the concepts, finding that concentration addition gives a reasonable worst case estimation in ecotoxicology even for substances with independent joint action.

Additive effects of herbicide combinations on aquatic non-target organisms

Abstract Assessments on combination effects are valid only with making clear reference to a definite and pharmacologically sound concept on expected effects. To test the predictive value of the concept of concentration addition, algal toxicities of 29 binary mixtures of 9 different pesticides were analyzed. For 85% of these mixtures results were consistent with concentration additivity. Thus, in case experimental data on the toxicity of a specific mixture are lacking, concentration additivity may be a reasonable assumption in hazard assessment procedures.

Comparative hazard identification for pesticides: interrelations between physico-chemical properties, tonnages, and occurrence in surface waters

Abstract For a set of 274 pesticides, the available information on basic physico-chemical properties (water solubility, vapour pressure, and Henrys law coefficient), agricultural usage in Germany (amounts sold and amounts applied) and occurrence in surface waters, bank filtrates and ground waters in the FRG was compiled. The analysis of these data confirmed that the potential of pesticide appearance in surface waters enlarges with increasing agricultural emission. However, the quality and the amount of available data did not allow a validation of the predictive value of fundamental physico-chemical variables which are used as indicators of exposure potentials for aquatic environments in hazard identification procedures and priority setting schemes. Thus, it is concluded that both registers of pesticide usage as well as systematic monitoring studies on residues in surface waters are needed in order to evaluate and improve the instruments of a predictive exposure assessment.

Ammonia rhythm in Microcystis firma studied by in vivo 15N and 31P NMR spectroscopy

Cultures of the cyanobacterium Microcystis firma show rhythmic uptake and release of ammonia under conditions of carbon limitation. The massive removal of ammonia from the medium during the first light phase has little impact on the intracellular pH: a pH shift of less than 0.2 U towards the alkaline can be measured by in vivo 31P NMR. Furthermore, the energy status of the cells remains regulated. In vivo 15N NMR of M. firma, cultivated either with labelled nitrate or ammonia as the sole nitrogen source, reveals only gradual differences in the pool of free amino acids. Additionally both cultivation types show γ-aminobutyric acid, acid amides and yet unassigned secondary metabolites as nitrogen storing compounds. Investigating the incorporation of nitrogen under carbon limitation, however, only the amide nitrogen of glutamine is found permanently labelled in situ. While transamination reactions are blocked, nitrate reduction to ammonia can still proceed. Cation exchange processes in the cell wall are considered regarding the ammonia disappearance in the first phase, and the control of ammonia uptake is discussed with respect to the avoidance of intracellular toxification.

Kombinationswirkungen in der aquatischen Toxikologie

Seit mehr als einem Jahrhundert ist die Analyse von Kombinations-effekten Gegenstand wissenschaftlicher Arbeiten in verschiedensten Disziplinen. Inzwischen werden zwei grundlegende Konzepte fur gultig gehalten: LOEWE-Additivitat (Konzentrations-Additivitat) und BLISS-Unabhangigkeit (Greco et al. 1992). In dieser Arbeit werden Ergebnisse eines Forschungsprojektes dargestellt, in dem 137 binare Kombinationen von Pestiziden und Tensiden in einem Algenbiotest untersucht wurden. Ziel des Vorhabens war es, die Vorhersagbarkeit von Kombinationseffekten zu prufen und Rationale fur eine prospektive Abschatzung von Mischungstoxizitaten in aquatischen Systemen zu entwickeln. Mit Hilfe eines entwickelten „index on prediction quality” wurden die Abstande zwischen beobachteten und erwarteten Kombinationstoxizitaten beurteilt. Als Ergebnis zeigte sich, das die Mischungstoxizitaten fur die meisten Kombinationsversuche durch LOEWE-Additivitat gut vorhergesagt werden konnten. Hierdurch bestatigt sich abermals, das dieses Konzept ein geeignetes Instrument auch fur rechtliche Regelungen darstellt. BLISS-Unabhangigkeit fuhrte indes fur viele Kombinationen ebenfalls zu guten Vorhersagen. Das Dilemma hinsichtlich der Frage, welches Konzept begrundet zur Vorhersage von Mischungstoxizitaten verwendet werden sollte, ist insbesondere bezuglich niedriger Stoffkonzentrationen bedeutsam. Gemas dem Konzept der BLISS-Unabhangigkeit sind namlich im Gegensatz zur LOEWE-Additivitat keine Kombinationseffekte fur Konzentrationen unterhalb einer stoffindividuellen NOEC zu erwarten. Die Frage, ob jeder Wirkstoff unabhangig von seiner Konzentration zur Gesamttoxizitat einer Kombination beitragt, bleibt daher derzeit noch offen.

Cell physiological parameters to detect ecotoxicological risks

Abstract The tendency to abandon classical toxicity tests with single species due to their inability to provide data to reliably predict responses on ecosystem levels and public pressure to use alternative simple and inexpensive bioassays on cellular and subcellular levels favours the use of cell physiological parameters to identify ecotoxicological risks. With the definition of basic biological principles valid for all complexity levels of life, from cells to ecosystems, it seems possible to develop from them basic indicatory parameters for ecosystem functioning and to provide measures to monitor it. As an example, the possible use of algal toxicity tests for the qualitative and quantitative analysis of physiological key functions is given, which may lead to improvements in ecotoxicological risk assessment.

In vivo NMR spectroscopy: in situ 15N pulse labelling NMR spectroscopy with photoautotrophic microorganisms

Abstract For studying the nitrogen metabolism in plants 15N NMR spectroscopy can be used. For in vivo 15N NMR (natural abundance of 15N: 0.37%) enrichment of the sample with the isotope 15N is compulsory. The detection of time courses of 15N assimilation from cells, which are enriched in culture is restricted in scope. Here, a method, the 15N pulse labelling NMR spectroscopy, is demonstrated, which permits labelling of different nitrogen compounds in photoautotrophic microorganisms during the NMR spectroscopic measurement. Using an effective illumination system it is possible to maintain photosynthesis in plant samples of high biomass densities in the magnet necessary for ammonia assimilation. The technique thus enables to directly observe ammonia assimilation pathways by application of a 15NO3 − or 15NH4 − pulses. Fur das Studium des Stickstoffstoffwechsels der Pflanzen kann die 15N-NMR-Spektroskopie herangezogen werden. Hierzu ist bei der in-vivo-15N-NMR (naturliche Haufigkeit von 15N: 0.37%) eine Anrei...