WP112 (DEW-1117-844307) Effects of isoproturon toxicity on alga Scenedesmus obliquus measured by chlorophyll a fluorescence parameters.
Start time: 8:00 AM
Dewez, D.¹, Drouin, J.¹, Popovic, R.¹, ¹ University of Quebec in Montreal, Department of Chemistry, Montreal, Quebec, Canada
Toxicity effect induced by isoproturon [3-(4-isopropylphenyl)-1, 1-dimethylurea] may deteriorate photosynthesis processes and consequently inhibit growth of non-target plant species. Therefore, this environmental stress will cause growth inhibition of different algal species. For isoproturon herbicide is known to inhibit photochemical and biochemical processes of photosynthesis which alters the physiological state of plant. Therefore, the photosynthetic activity represents a convenient method to evaluate isoproturon toxicity effect. The change of photosynthetic fluorescence parameters of Scenedesmus obliquus affected by isoproturon have been evaluated by using plant efficiency analyzer (PEA) and Pulse Amplitude Modulated (PAM) fluorometer. When Scenedesmus obliquus was exposed to isoproturon concentration from 37-300 nM, the inhibition of photosystem II electron transport was associated with plastoquinone reduction process. However, at higher concentration of isoproturon (1200-2400 nM), the PSII water splitting system was also inhibited. This type of inhibition was indicated by the change of different fluorescence parameters. The most sensitive parameters indicating isoproturon toxicity effect were photosystem II photochemical functional yield (S) and non-photochemical quenching value (Q_N). In this report we discussed the possible inhibition site of isoproturon effect and the suitability of photosystem II fluorescence parameters to be used as toxicity biomarkers.

WP113 (ARM-1117-578038) Fate and toxicity of oil sands naphthenic acids in wetland plants.
Start time: 8:00 AM
Armstrong, S^{1, 2}, Headley, J¹, Peru, K¹, Germida, J², ¹ National Water Research Institute, Saskatoon, Saskatchewan, Canada² Department of Soil Science, University of Saskatchewan, Saskatoon, Saskatchewan, Canada
Naphthenic acids (NAs) are alkyl-substituted cycloaliphatic carboxylic acids or acyclic aliphatic acids and are released from bitumen during the mining of oil sands and the processing of bitumen for oil production. Naphthenic acids are of toxicological concern in the environment because they have acute aquatic toxicity to a variety of fish species. Removal of recalcitrant organics like NAs from tailings pond water has proved to be a challenge. This study investigated the strategy of using plants to remediate naphthenic acids; a process known as phytoremediation. A variety of native emergent and submergent macrophytes [cattails (Typha latifolia), common reed grass (Phragmites australis), common bulrush (Scirpus lacustris ), and northern milfoil (Myriophyllum sibiricum)] were grown hydroponically in the presence NAs. Toxic effects in the plants were recorded and the NA concentration in the hydroponic nutrient media was monitored over time using negative ion electrospray ionization mass spectrometry. There was sustained sorption and/or uptake along with saturation in NA treatments containing wetland plants. Preliminary results indicate that there is little or no selectivity in the distribution of naphthenic acid components that are sorbed/sequested by the wetland plants under laboratory conditions. Wetland plants grown in the laboratory appeared to be more sensitive to levels of naphthenic acids (< 70 mg L^-1) compared to those reported for natural field environments.

WP114 (BAR-1117-838681) Viability and antioxidant responses of the dinoflagellate Lingulodinium polyedrum upon molybdenum bioavailability in seawater.
Start time: 8:00 AM
Barros, M¹, Soares, C¹, Glavina, A¹, Colepicolo, P², ¹ Universidade Cruzeiro do Sul (Unicsul), Sao Paulo, SP, Brazil² Universidade de São Paulo (USP), Sao Paulo, SP, Brazil
Molybdenum (Mo) is a transition metal used primarily (90% or more) as an additive to steel and corrosion-resistant alloys in metallurgical industries. As catalytic center of some redox enzymes, Mo is an essential element for inorganic nitrogen assimilation/fixation and phytohormone synthesis in photosynthesizing species, and the metabolism of reactive oxygen and nitrogen species (ROS/RNS) in both plant and animal cells. Thus, provoked by uncontrolled industrial waste releases in freshwater or seawater, it is plausible that excessive availability of water-soluble molybdate anions would hypothetically alter microalgal populations in specific aquatic environments. In oceanic and estuarine waters, the availability of Mo is severely limited through complex sorption-reduction reactions in sulfide-rich sediments. In the water column, the microalgal absorption of molybdate is supposedly inhibited by uptake competition with sulfate ions, a much more abundant anion in seawater (c.a. 25 mM). Accordingly, this work examines the effects of micromolar concentrations of molybdate (0.1 to 200 M) in the ROS/RNS and nitrogen metabolism of the dinoflagellate Lingulodinium polyedrum, under concomitant interference of different concentrations of sulfate or ferrous sulfide (FeS). L.polyedrum cultures grown in 25 mM sulfate and molybdate-depleted medium showed approximately the same growth rate as regular laboratory maintaining cultures until the fifth day, whereas culture media containing 3.5 or 9.6 mM sulfate drastically inhibited algal growth. In 0.1 g.L^-1 FeS-added cultures, higher antioxidant enzyme activities (as parameters of oxidative stress) were measured in cultures treated with 50 M molybdate, whereas comparable levels were only found in 0.5 g.L^-1 FeS-added dinoflagellate cultures containing 100 M molybdate. Despite several studies have demonstrated the (eco-)toxicological effects of Mo⁶⁺ forms in algal cells, our results suggest that environmental factors (such as local sediment composition and effective sulfate concentration in the water column) must be considered in order to fully understand phytoplankton community dynamics and metal contamination in seawater. Financial support: CNPq and FAPESP (Brazil); IFS (Sweden).

WP116 (VAL-1117-095219) Time-varying exposure of algae to herbicides with different modes of action: effects at the population and subcellular level.
Start time: 8:00 AM
Vallotton, N¹, Escher, B¹, Eggen, R¹, Chèvre, N¹, ¹ EAWAG, Duebendorf, Switzerland
Several studies have highlighted the dynamics of pesticide concentrations in rivers during and after field application periods. Water quality criteria for pesticides are often exceeded for short periods of time. During these periods herbicides, in particular, can reach very high levels. Further, many substances are usually detected simultaneously. Standard laboratory toxicity tests with algae generally use constant exposure and are not suitable to evaluate the toxicity of such pulses and/or repeated exposure. The aim of our research is to investigate the effects on green algae of high concentrations of one or several herbicides after short-time exposure in order to simulate rain events. Experimentally, algae are exposed from 10h up to 2 days to realistic herbicide concentrations, i.e. those typically measured during field studies. The effects of these short exposures are measured at the subcellular level (effects on photosynthesis activity) and at the population level (growth rate). Our results show that photosystem inhibitor herbicides (atrazine and isoproturon) affect the photosynthetic activity very rapidly before any effects on growth rate can be detected. Exposure to high concentrations induces a strong inhibition of the photosynthesis as well as growth inhibition. When placed back in uncontaminated medium the algae recover rapidly. On the other hand, short exposure to the chloroacetanilide herbicide S-metolachlor indicates that this substance affects the growth rate, but not the photosynthetic activity. Furthermore, the cell size increases during the exposure, and the recovery in uncontaminated medium is uncertain.

WP117 (HOT-1117-841332) Evaluation of test acceptability criteria for the giant kelp toxicity test.
Start time: 8:00 AM
Hotz, A¹, Bailey, H¹, ¹ Nautilus Environmental, San Diego, CA, USA
The giant kelp toxicity test was originally developed by the Marine Bioassay Project in 1990, and adopted by US EPA in 1995 as part of a suite of chronic toxicity tests for west coast species. Acceptability criteria for this test were largely based on data collected during the Marine Bioassay Project, and have not been evaluated since. This study evaluated reference toxicant test data from five laboratories in Southern California in order to determine whether the criteria are sufficiently robust to be applied across a range of testing laboratories. Comparisons and conclusions will be presented.