The combined SPE:ToxY-PAM phytotoxicity assay; application and appraisal of a novel biomonitoring tool for the aquatic environment

Application of biological early warning systems in wastewater treatment plants: Introducing a promising approach to monitor changing wastewater composition

Wastewater treatment plants (WWTPs) are a major source of micropollutants to surface waters. Currently, their chemical or biological monitoring is realized by using grab or composite samples, which provides only snapshots of the current wastewater composition. Especially in WWTPs with industrial input, the wastewater composition can be highly variable and a continuous assessment would be advantageous, but very labor and cost intensive. A promising concept are automated real-time biological early warning systems (BEWS), where living organisms are constantly exposed to the water and an alarm is triggered if the organism's responses exceed a harmful threshold of acute toxicity. Currently, BEWS are established for drinking water and surface water but are seldom applied to monitor wastewater. This study demonstrates that a battery of BEWS using algae (Chlorella vulgaris in the Algae Toximeter, bbe Moldaenke), water flea (Daphnia magna in the DaphTox II, bbe Moldaenke) and gammarids (Gammarus pulex in the Sensaguard, REMONDIS Aqua) can be adapted for wastewater surveillance. For continuous low-maintenance operation, a back-washable membrane filtration system is indispensable for adequate preparation of treated wastewater. Only minor deviations in the reaction of the organisms towards treated and filtered wastewater compared to surface waters were detected. After spiking treated wastewater with two concentrations of the model compounds diuron, chlorpyrifos methyl, and sertraline, the organisms in the different BEWS showed clear responses depending on the respective compound, concentration and mode of action. Immediate effects on photosynthetic activity of algae were detected for diuron exposure, and strong behavioral changes in water flea and gammarids after exposure to chlorpyrifos methyl or sertraline were observed, which triggered automated alarms. Different types of data analysis were applied to extract more information out of the specific behavioral traits, than only provided by the vendors algorithms. To investigate, whether behavioral movement changes can be linked to impact other endpoints, the effects on feeding activity of G. pulex were evaluated and results indicated significant differences between the exposures. Overall, these findings provide an important basis indicating that BEWS have the potential to act as alarm systems for pollution events in the wastewater sector.

Toxicity of the herbicides diuron, propazine, tebuthiuron, and haloxyfop to the diatom Chaetoceros muelleri

Conventional photosystem II (PSII) herbicides applied in agriculture can pose significant environmental risks to aquatic environments. In response to the frequent detection of these herbicides in the Great Barrier Reef (GBR) catchment area, transitions towards 'alternative' herbicides are now widely supported. However, water quality guideline values (WQGVs) for alternative herbicides are lacking and their potential ecological impacts on tropical marine species are generally unknown. To improve our understanding of the risks posed by some of these alternative herbicides on marine species under tropical conditions, we tested the effects of four herbicides on the widely distributed diatom Chaetoceros muelleri. The PSII herbicides diuron, propazine, and tebuthiuron induced substantial reductions in both 24 h effective quantum yields (ΔF/Fm') and 3-day specific growth rates (SGR). The effect concentrations, which reduced ΔF/Fm' by 50% (EC50), ranged from 4.25 µg L-1 diuron to 48.6 µg L-1 propazine, while the EC50s for SGR were on average threefold higher, ranging from 12.4 µg L-1 diuron to 187 µg L-1 tebuthiuron. Our results clearly demonstrated that inhibition of ΔF/Fm' in PSII is directly linked to reduced growth (R2 = 0.95) in this species, further supporting application of ΔF/Fm' inhibition as a valid bioindicator of ecological relevance for PSII herbicides that could contribute to deriving future WQGVs. In contrast, SGR and ΔF/Fm' of C. muelleri were nonresponsive to the non-PSII herbicide haloxyfop at the highest concentration tested (4570 µg L-1), suggesting haloxyfop does not pose a risk to C. muelleri. The toxicity thresholds (e.g. no effect concentrations; NECs) identified in this study will contribute to the derivation of high-reliability marine WQGVs for some alternative herbicides detected in GBR waters and support future assessments of the cumulative risks of complex herbicide mixtures commonly detected in coastal waters.

Toxicity of ten herbicides to the tropical marine microalgae Rhodomonas salina

Herbicide contamination of nearshore tropical marine ecosystems is widespread and persistent; however, risks posed by most ‘alternative’ herbicides to tropical marine microalgae remain poorly understood. Experimental exposures of the important but understudied microalgae Rhodomonas salina to seven individual Photosystem II (PSII) inhibitor herbicides (diuron, metribuzin, hexazinone, tebuthiuron, bromacil, simazine, propazine) led to inhibition of effective quantum yield (ΔF/F_m′) and subsequent reductions in specific growth rates (SGR). The concentrations which reduced ΔF/F_m′ by 50% (EC₅₀) ranged from 1.71-59.2 µg L⁻¹, while the EC₅₀s for SGR were 4-times higher, ranging from 6.27-188 µg L⁻¹. Inhibition of ΔF/F_m′ indicated reduced photosynthetic capacity, and this correlated linearly with reduced SGR (R² = 0.89), supporting the application of ∆F/F_m’ inhibition as a robust and sensitive indicator of sub-lethal toxicity of PSII inhibitors for this microalga. The three non-PSII inhibitor herbicides (imazapic, haloxyfop and 2,4-Dichlorophenoxyacetic acid (2,4-D)) caused low or no toxic responses to the function of the PSII or growth at the highest concentrations tested suggesting these herbicides pose little risk to R. salina. This study highlights the suitability of including R. salina in future species sensitivity distributions (SSDs) to support water quality guideline development for the management of herbicide contamination in tropical marine ecosystems.

Identification of algal growth inhibitors in treated waste water using effect-directed analysis based on non-target screening techniques

Growth inhibition of freshwater microalga Pseudokirchneriella subcapitata caused by a waste water treatment plant (WWTP) effluent extract was investigated using an effect directed analysis (EDA) approach. The objective was to identify compounds responsible for the toxicity by combining state-of-the-art sampling, bioanalytical, fractionation and non-target screening techniques. Three fractionation steps of the whole extract were performed and bioactive fractions were analysed with GC (xGC)-MS and LC-HRMS. In total, 383 compounds were tentatively identified, and their toxicity was characterized using US EPA Ecotox database, open scientific literature or modelled by ECOSAR. Among the top-ranking drivers of toxicity were pesticides and their transformation products, pharmaceuticals (barbiturate derivatives and macrolide antibiotics e.g. azithromycin), industrial compounds or caffeine and its metabolites. Several of the top-ranking pesticides are no longer registered for use in plant protection products or biocides in the Czech Republic (e.g. prometryn, atrazine, acetochlor, resmethrin) and some are approved only for use in biocides (e.g. terbutryn, carbendazim, phenothrin), which indicates that their non-agricultural input into aquatic environment via WWTPs should be carefully considered. The study demonstrated a functional strategy of combining biotesting, fractionation and non-target screening techniques in the EDA study focused on the identification of algal growth inhibitors in WWTP effluent.

Microcystins and cyanophyte extracts inhibit or promote the photosynthesis of fluvial algae. Ecological and management implications

The ecological influence of cyanotoxins on aquatic biota remains unclear despite the numerous published references on toxicological and sanitary problems related with cyanophyte proliferation. The effects of microcystins and cyanophyte extracts on the photosynthesis of the algae that belong to two taxonomic groups, Rhodophyta and Bacillariophyta, were studied in an attempt to elucidate their role in the intraspecific competence and physiognomy of fluvial communities. The data showed that both cyanobacteria extracts and pure microcystin-LR affected the photosynthetic activity of all the tested organisms, diatoms (Fistulifera pelliculosa, Gomphonema parvulum, Nitzschia frustulum and Stephanodiscus minutulus) and red algae (Chroothece richteriana) at environmentally relevant concentrations. Effects varied with strains and time, and promoted or inhibited photosynthesis. The microcystins and the other compounds present in cyanobacteria extracts may explain the competence effects observed in nature, especially in calcareous environments where they predominate, and after disturbing events like heavy rains or floods, which may destroy cyanophyte mats and release toxic or inhibitory compounds in a seasonal scale pattern.

Australia's pesticide environmental risk assessment failure: the case of diuron and sugarcane

In November 2012, the Australian Pesticide and Veterinary Medicines Authority (APVMA) concluded a 12 year review of the PSII herbicide diuron. One of the primary concerns raised during the review was the potential impact on aquatic ecosystems, particularly in the catchments draining to the Great Barrier Reef. The environmental risk assessment process used by the APVMA utilised a runoff risk model developed and validated under European farming conditions. However, the farming conditions in the sugarcane regions of the Great Barrier Reef catchments have environmental parameters beyond the currently validated bounds of the model. The use of the model to assess environmental risk in these regions is therefore highly inappropriate, demonstrating the pitfalls of a one size fits all approach.

Realistic environmental mixtures of micropollutants in surface, drinking, and recycled water: herbicides dominate the mixture toxicity toward algae

Mixture toxicity studies with herbicides have focused on a few priority components that are most likely to cause environmental impacts, and experimental mixtures were often designed as equipotent mixtures; however, real-world mixtures are made up of chemicals with different modes of toxic action at arbitrary concentration ratios. The toxicological significance of environmentally realistic mixtures has only been scarcely studied. Few studies have simultaneously compared the mixture effect of water samples with designed reference mixtures comprised of the ratios of analytically detected concentrations in toxicity tests. In the present study, the authors address the effect of herbicides and other chemicals on inhibition of photosynthesis and algal growth rate. The authors tested water samples including secondary treated wastewater effluent, recycled water, drinking water, and storm water in the combined algae assay. The detected chemicals were mixed in the concentration ratios detected, and the biological effects of the water samples were compared with the designed mixtures of individual detected chemicals to quantify the fraction of effect caused by unknown chemicals. The results showed that herbicides dominated the algal toxicity in these environmentally realistic mixtures, and the contribution by the non-herbicides was negligible. A 2-stage model, which used concentration addition within the groups of herbicides and non-herbicides followed by the model of independent action to predict the mixture effect of the two groups, could predict the experimental mixture toxicity effectively, but the concentration addition model for herbicides was robust and sufficient for complex mixtures. Therefore, the authors used the bioanalytical equivalency concept to derive effect-based trigger values for algal toxicity for monitoring water quality in recycled and surface water. All water samples tested would be compliant with the proposed trigger values associated with the appropriate guidelines.

Phytotoxicity of four photosystem II herbicides to tropical seagrasses

Coastal waters of the Great Barrier Reef (GBR) are contaminated with agricultural pesticides, including the photosystem II (PSII) herbicides which are the most frequently detected at the highest concentrations. Designed to control weeds, these herbicides are equally potent towards non-target marine species, and the close proximity of seagrass meadows to flood plumes has raised concerns that seagrasses may be the species most threatened by herbicides from runoff. While previous work has identified effects of PSII herbicides on the photophysiology, growth and mortality in seagrass, there is little comparative quantitative toxicity data for seagrass. Here we applied standard ecotoxicology protocols to quantify the concentrations of four priority PSII herbicides that inhibit photochemistry by 10, 20 and 50% (IC₁₀, IC₂₀ and IC₅₀) over 72 h in two common seagrass species from the GBR lagoon. The photosystems of seagrasses Zosteramuelleri and Haloduleuninervis were shown to be generally more sensitive to the PSII herbicides Diuron, Atrazine, Hexazinone and Tebuthiuron than corals and tropical microalgae. The herbicides caused rapid inhibition of effective quantum yield (∆F/F_m′), indicating reduced photosynthesis and maximum effective yields (F_v/F_m) corresponding to chronic damage to PSII. The PSII herbicide concentrations which affected photosynthesis have been exceeded in the GBR lagoon and all of the herbicides inhibited photosynthesis at concentrations lower than current marine park guidelines. There is a strong likelihood that the impacts of light limitation from flood plumes and reduced photosynthesis from PSII herbicides exported in the same waters would combine to affect seagrass productivity. Given that PSII herbicides have been demonstrated to affect seagrass at environmental concentrations, we suggest that revision of environmental guidelines and further efforts to reduce PSII herbicide concentrations in floodwaters may both help protect seagrass meadows of the GBR from further decline.

Phytotoxicity induced in isolated zooxanthellae by herbicides extracted from Great Barrier Reef flood waters

To date there has been limited evidence anthropogenically sourced pollution from catchments reaching corals of the Great Barrier Reef (GBR). In this study, freshly isolated zooxanthellae were exposed to polar chemicals (chiefly herbicides) extracted from water samples collected in a flood plume in the GBR lagoon. Photosynthetic potential of the isolated zooxanthellae declined after exposure to concentrated extracts (10 times) from all but one of the sampling sites. Photosynthetic potential demonstrated a significant positive relationship with the concentration of diuron in the concentrated extracts and a significant inverse relationship with salinity measured at the sampling site. This study demonstrates that runoff from land based application of herbicides may reduce photosynthetic efficiency in corals of inshore reefs in the GBR. The ecological impacts of the chemicals in combination with other potential stressors on corals remain unclear.

Assessing the additive risks of PSII herbicide exposure to the Great Barrier Reef

Herbicide residues have been measured in the Great Barrier Reef lagoon at concentrations which have the potential to harm marine plant communities. Monitoring on the Great Barrier Reef lagoon following wet season discharge show that 80% of the time when herbicides are detected, more than one are present. These herbicides have been shown to act in an additive manner with regards to photosystem-II inhibition. In this study, the area of the Great Barrier Reef considered to be at risk from herbicides is compared when exposures are considered for each herbicide individually and also for herbicide mixtures. Two normalisation indices for herbicide mixtures were calculated based on current guidelines and PSII inhibition thresholds. The results show that the area of risk for most regions is greatly increased under the proposed additive PSII inhibition threshold and that the resilience of this important ecosystem could be reduced by exposure to these herbicides.

Additive toxicity of herbicide mixtures and comparative sensitivity of tropical benthic microalgae

Natural waters often contain complex mixtures of unknown contaminants potentially posing a threat to marine communities through chemical interactions. Here, acute effects of the photosystem II-inhibiting herbicides diuron, tebuthiuron, atrazine, simazine, and hexazinone, herbicide breakdown products (desethyl-atrazine (DEA) and 3,4-dichloroaniline (3,4-DCA)) and binary mixtures, were investigated using three tropical benthic microalgae; Navicula sp. and Cylindrotheca closterium (Ochrophyta) and Nephroselmis pyriformis (Chlorophyta), and one standard test species, Phaeodactylum tricornutum (Ochrophyta), in a high-throughput Maxi-Imaging-PAM bioassay (Maxi-IPAM). The order of toxicity was; diuron > hexazinone > tebuthiuron > atrazine > simazine > DEA > 3,4-DCA for all species. The tropical green alga N. pyriformis was up to 10-fold more sensitive than the diatoms tested here and reported for coral symbionts, and is recommended as a standard tropical test species for future research. All binary mixtures exhibited additive toxicity, and the use of herbicide equivalents (HEq) is therefore recommended in order to incorporate total-maximum-load measures for environmental regulatory purposes.

Predicting water toxicity: pairing passive sampling with bioassays on the Great Barrier Reef

Many coral reefs worldwide occur adjacent to urban or agricultural land which places these ecosystems at threat of exposure to complex mixtures of pollutants. In this study, the pairing of passive sampler extracts with bioassays is proposed as a tool for predicting effects of organic pollutant mixtures on key biota within coral reef ecosystems. Passive samplers, SDB-RPS Empore disks, which sequester a mixture of the contaminants present in the environment, were deployed at three sites in the Great Barrier Reef (GBR). Extracts from these samplers were analysed for herbicides and applied to bioassays targeting integral life stages or functions of coral reef biota. Biota included scleractinian coral larvae, sea urchin larvae, a marine diatom and marine bacteria. Photosynthesis in the marine diatom Phaeodactylum tricornutum was inhibited at the sampled environmental concentration while an environmental concentration factor of 15 times inhibited luminescence in the marine bacterium Vibrio fischeri. Concentrations of 50 times sampled environmental levels of organic pollutants inhibited >90% of Acropora millepora settlement and 100-fold environmental enrichment inhibited 100% Heliocidaris tuberculata larval development. These results demonstrate the utility of pairing passive sampling with bioassays and reveal that mixtures of organic pollutants in the GBR have the potential to cause detrimental effects to coral reef biota.

Identification and characterization of freshwater algae from a pollution gradient using rbcL sequencing and toxicity testing

One approach in toxicity testing using microalgae is to assess the modulation of light energy absorbed as a result of exposure to contaminants. In this study, four strains of microalgae were isolated to obtain a variety of taxa for testing from sites receiving various levels of environmental stressors around Christchurch, New Zealand. The strains were characterized by partially sequencing rbcL, a routinely used gene in plant phylogenetics with a large existing database of strains. Based on morphological observation and gene sequences, the strains were identified as Chlorella sp., Neochloris sp., and Choricystis minor. The isolates were exposed to the herbicide glyphosate and the metal zinc, and their responses were measured using the ToxY-PAM system. Chlorella sp. was the most sensitive. Two strains of Choricystis minor were isolated from different ponds in an effluent gradient at a sewage treatment plant. Analysis of variance indicated that the isolate from the least contaminated pond was more sensitive to zinc (although regression analysis did not show this result). This suggests that the selective pressure exerted on algal strains by a contamination gradient over short a distance is detectable by both genetic and physiological methods, with implications for sourcing appropriate indicator organisms from the environment.

Development of a toxicity identification evaluation protocol using chlorophyll-a fluorescence in a marine microalga

Growth inhibition bioassays with the microalga Nitzschia closterium have recently been applied in marine Toxicity Identification Evaluation (TIE) testing. However, the 48-h test duration can result in substantial loss of toxicants over time, which might lead to an underestimation of the sample toxicity. Although shorter-term microalgal bioassays can minimize such losses, there are few bioassays available and none are adapted for marine TIE testing. The acute (5-min) chlorophyll-a fluorescence bioassay is one alternative; however, this bioassay was developed for detecting herbicides in freshwater aquatic systems and its suitability for marine TIE testing was not known. In this study, a chlorophyll-a fluorescence bioassay using the marine microalga Isochrysis galbana was able to detect contaminants other than herbicides at environmentally relevant concentrations and tolerated the physical and chemical manipulations needed for a Phase I TIE. Phase I TIE procedures were successfully developed using this chlorophyll-a fluorescence bioassay and used to identify all classes of contaminants present in a synthetic mixture of known chemical composition. In addition, TIEs with both the acute fluorescence bioassay and the standard growth inhibition bioassay identified the same classes of toxicants in a sample of an unknown complex effluent. Even though the acute chlorophyll-a fluorescence end point was less sensitive than the chronic cell division end point, TIEs with the chlorophyll-a fluorescence bioassay provided a rapid and attractive alternative to longer-duration bioassays.

Comparative effects of herbicides on photosynthesis and growth of tropical estuarine microalgae

Pulse amplitude modulation (PAM) fluorometry is ideally suited to measure the sub-lethal impacts of photosystem II (PSII)-inhibiting herbicides on microalgae, but key relationships between effective quantum yield [Y(II)] and the traditional endpoints growth rate (micro) and biomass increase are unknown. The effects of three PSII-inhibiting herbicides; diuron, hexazinone and atrazine, were examined on two tropical benthic microalgae; Navicula sp. (Heterokontophyta) and Nephroselmis pyriformis (Chlorophyta). The relationships between Y(II), micro and biomass increase were consistent (r2 > or =0.90) and linear (1:1), validating the utility of PAM fluorometry as a rapid and reliable technique to measure sub-lethal toxicity thresholds of PSII-inhibiting herbicides in these microalgae. The order of toxicity (EC50 range) was: diuron (16-33 nM) > hexazinone (25-110 nM) > atrazine (130-620 nm) for both algal species. Growth rate and photosynthesis were affected at diuron concentrations that have been detected in coastal areas of the Great Barrier Reef.

Toxic equivalent concentrations (TEQs) for baseline toxicity and specific modes of action as a tool to improve interpretation of ecotoxicity testing of environmental samples

The toxic equivalency concept is a widely applied method to express the toxicity of complex mixtures of compounds that act via receptor-mediated mechanisms such as induction of the arylhydrocarbon or estrogen receptors. Here we propose to extend this concept to baseline toxicity, using the bioluminescence inhibition test with Vibrio fischeri, and an integrative ecotoxicity endpoint, algal growth rate inhibition. Both bioassays were validated by comparison with literature data and quantitative structure-activity relationships (QSARs) for baseline toxicity were developed for all endpoints. The novel combined algae test, with Pseudokirchneriella subcapitata, allows for the simultaneous evaluation of specific inhibition of photosynthesis and growth rate. The contributions of specific inhibition of photosynthesis and non-specific toxicity could be differentiated by comparing the time and endpoint pattern. Photosynthesis efficiency, measured with the saturation pulse method after 2 h of incubation, served as indicator of specific inhibition of photosynthesis by photosystem II inhibitors. Diuron equivalents were defined as toxicity equivalents for this effect. The endpoint of growth rate over 24 h served to derive baseline toxicity equivalent concentrations (baseline-TEQ). By performing binary mixture experiments with reference compounds and complex environmental samples from a sewage treatment plant and a river, the TEQ concept was validated. The proposed method allows for easier interpretation and communication of effect-based water quality monitoring data and provides a basis for comparative analysis with chemical analytical monitoring.

Biomaterial culture conditions impacting the performance of a PAM fluorometry based aquatic phytotoxicity assay

An aquatic phytotoxicity assay, based on the principles of pulse amplitude modulated (PAM) fluorometry has recently been developed and validated under laboratory conditions. Characteristics of the assay include the use of photosynthesising biomaterial, most frequently whole organism microalgae. The instrument employs light probing measurements to monitor chlorophyll fluorescence signals emitted by the biomaterial component. These characteristics could leave assay performance susceptible to interference by minor variations in biomaterial treatment and culture conditions prior to testing. This study investigates assay performance in response to variations in two microalgae culture parameters; short-term light history (24h) prior to testing and the sterility of long-term culture conditions. Light history of the four microalgal species tested significantly impacted their toxicity response, as measured with the assay. Light treatments of 5 micromol photons m(-2)s(-1) produced the highest photosystem II quantum yields (Phi(II)) whilst higher light intensities resulted in an inverse relationship between Phi(II) and the measured toxicity response (inhibition (%) of photochemistry). Of the two microalgal cultures tested, sterility of culture conditions significantly impacted the performance of the green freshwater algae, Chlorella vulgaris as assay biomaterial. On average 1 microg L(-1) diuron inhibited photochemistry 2.6% less in axenically cultured C. vulgaris compared with non-axenically maintained cultures. This investigation series contributes valuable quality assurance data towards microalgal based PAM fluorometry assays and emphasises the importance of such investigations if new biorecognition systems are to be accredited and/or routinely incorporated for biomonitoring purposes.

Combining passive sampling and toxicity testing for evaluation of mixtures of polar organic chemicals in sewage treatment plant effluent

Effluent from sewage treatment plants has been associated with a range of pollutant effects. Depending on the influent composition and treatment processes the effluent may contain a myriad of different chemicals which makes monitoring very complex. In this study we aimed to monitor relatively polar organic pollutant mixtures using a combination of passive sampling techniques and a set of biochemistry based assays covering acute bacterial toxicity (Microtox), phytotoxicity (Max-I-PAM assay) and genotoxicity (umuC assay). The study showed that all of the assays were able to detect effects in the samples and allowed a comparison of the two plants as well as a comparison between the two sampling periods. Distinct improvements in water quality were observed in one of the plants as result of an upgrade to a UV disinfection system, which improved from 24x sample enrichment required to induce a 50% response in the Microtox assay to 84x, from 30x sample enrichment to induce a 50% reduction in photosynthetic yield to 125x, and the genotoxicity observed in the first sampling period was eliminated. Thus we propose that biochemical assay techniques in combination with time integrated passive sampling can substantially contribute to the monitoring of polar organic toxicants in STP effluents.

Phytotoxicity of surface waters of the Thames and Brisbane River Estuaries: A combined chemical analysis and bioassay approach for the comparison of two systems

The Thames Estuary, UK, and the Brisbane River, Australia, are comparable in size and catchment area. Both are representative of the large and growing number of the world's estuaries associated with major cities. Principle differences between the two systems relate to climate and human population pressures. In order to assess the potential phytotoxic impact of herbicide residues in the estuaries, surface waters were analysed with a PAM fluorometry-based bioassay that employs the photosynthetic efficiency (photosystem II quantum yield) of laboratory cultured microalgae, as an endpoint measure of phytotoxicity. In addition, surface waters were chemically analysed for a limited number of herbicides. Diuron, atrazine and simazine were detected in both systems at comparable concentrations. In contrast, bioassay results revealed that whilst detected herbicides accounted for the observed phytotoxicity of Brisbane River extracts with great accuracy, they consistently explained only around 50% of the phytotoxicity induced by Thames Estuary extracts. Unaccounted for phytotoxicity in Thames surface waters is indicative of unidentified phytotoxins. The greatest phytotoxic response was measured at Charing Cross, Thames Estuary, and corresponded to a diuron equivalent concentration of 180 ng L(-1). The study employs relative potencies (REP) of PSII impacting herbicides and demonstrates that chemical analysis alone is prone to omission of valuable information. Results of the study provide support for the incorporation of bioassays into routine monitoring programs where bioassay data may be used to predict and verify chemical contamination data, alert to unidentified compounds and provide the user with information regarding cumulative toxicity of complex mixtures.

Passive sampling of herbicides combined with effect analysis in algae using a novel high-throughput phytotoxicity assay (Maxi-Imaging-PAM)

We propose to combine a passive sampler for polar organic compounds (POS) with a specific bioassay for phytotoxicity to assess the hazard of herbicidal compounds in surface waters. The POS consisted of an Empore disk coated with styrenedivinylbenzene deployed in a Teflon housing, which has relatively high sampling rates (e.g., approximately 1 L d(-1) for diuron). POS were deployed for 5 days in a small-scale field study in South East Queensland, Australia, in a relatively pristine environment and an urban environment to explore sensitivity towards herbicides and potential influences of non-herbicidal pollutants. Besides chemical analysis of 8 herbicides, a novel bioassay (Maxi-Imaging-PAM, IPAM) was employed to assess the phytotoxic effects of water samples and POS extracts. The IPAM allows rapid assessment of photosynthetic quantum yields of a large number of samples via chlorophyll-fluorescence imaging and the saturation pulse method. Sampling rates for several herbicides from laboratory calibrations were found to be applicable under field conditions. Toxic equivalent concentrations (with reference to the herbicide diuron) were computed from the concentrations determined by chemical analysis and the relative potency (also termed toxic equivalence factor) of the detected herbicides. There was good agreement between diuron equivalent concentrations from chemical analysis and diuron equivalent concentrations determined with the IPAM.

The selection of a model microalgal species as biomaterial for a novel aquatic phytotoxicity assay

A phytotoxicity assay based on the ToxY-PAM dual-channel yield analyser has been developed and successfully incorporated into field assessments for the detection of phytotoxicants in water. As a means of further exploring the scope of the assay application and of selecting a model biomaterial to complement the instrument design, nine algal species were exposed to four chemical substances deemed of priority for water quality monitoring purposes (chlorpyrifos, copper, diuron and nonylphenol ethoxylate). Inter-species differences in sensitivity to the four toxicants varied by a factor of 1.9-100. Measurements of photosystem-II quantum yield using these nine single-celled microalgae as biomaterial corroborated previous studies which have shown that the ToxY-PAM dual-channel yield analyser is a highly sensitive method for the detection of PS-II impacting herbicides. Besides Phaeodactylum tricornutum, the previously applied biomaterial, three other species consistently performed well (Nitzschia closterium, Chlorella vulgaris and Dunaliella tertiolecta) and will be used in further test optimisation experiments. In addition to sensitivity, response time was evaluated and revealed a high degree of variation between species and toxicants. While most species displayed relatively weak and slow responses to copper, C. vulgaris demonstrated an IC10 of 51 microgL-1, with maximum response measured within 25 minutes and inhibition being accompanied by a large decrease in fluorescence yield. The potential for this C. vulgaris-based bioassay to be used for the detection of copper is discussed. There was no evidence that the standard ToxY-PAM protocol, using these unicellular algae species, could be used for the detection of chlorpyrifos or nonylphenol ethoxylate at environmentally relevant levels.

Application of a novel phytotoxicity assay for the detection of herbicides in Hervey Bay and the Great Sandy Straits

A novel phytotoxicity assay was incorporated into an environmental assessment of Hervey Bay and the Great Sandy Straits, to investigate the role of run-off associated herbicides in the deteriorated health of intertidal seagrass meadows. Dose response curves of common herbicides were performed and their toxicity equivalents elucidated to assist in analysis. The results of the assay were reproducible and corresponded strongly with results of chemical analyses. The incorporation of the assay into the assessment of surface waters added an important aspect to the study by allowing investigation of the toxicity of cumulative herbicide concentrations and yielding biologically relevant data. The highest herbicide concentration detected during the study was equivalent to 0.23 microg l(-1) diuron; a concentration known to inhibit photosynthetic efficiency of the assay biomaterial by approximately 3%.