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Water quality of the Great Barrier Reef (GBR) is determined by a range of natural and anthropogenic drivers that are resolved in the eReefs coupled hydrodynamic - biogeochemical marine model forced by a process-based catchment model, GBR Dynamic SedNet. Model simulations presented here quantify the impact of anthropogenic catchment loads of sediments and nutrients on a range of marine water quality variables. Simulations of 2011-2018 show that reduction of anthropogenic catchment loads results in improved water quality, especially within river plumes. Within the 16 resolved river plumes, anthropogenic loads increased chlorophyll concentration by 0.10 (0.02-0.25) mg Chl m -3 . Reductions of anthropogenic loads following proposed Reef 2050 Water Quality Improvement Plan targets reduced chlorophyll concentration in the plumes by 0.04 (0.01-0.10) mg Chl m -3 . Our simulations demonstrate the impact of anthropogenic loads on GBR water quality and quantify the benefits of improved catchment management., (Crown Copyright © 2021. Published by Elsevier Ltd. All rights reserved.)

Advanced water treatment of secondary treated effluent requires stringent quality control to achieve a water quality suitable for augmenting drinking water supplies. The removal of micropollutants such as pesticides, industrial chemicals, endocrine disrupting chemicals (EDC), pharmaceuticals, and personal care products (PPCP) is paramount. As the concentrations of individual contaminants are typically low, frequent analytical screening is both laborious and costly. We propose and validate an approach for continuous monitoring by applying passive sampling with Empore disks in vessels that were designed to slow down the water flow, and thus uptake kinetics, and ensure that the uptake is only marginally dependent on the chemicals' physicochemical properties over a relatively narrow molecular size range. This design not only assured integrative sampling over 27 days for a broad range of chemicals but also permitted the use of a suite of bioanalytical tools as sum parameters, representative of mixtures of chemicals with a common mode of toxic action. Bioassays proved to be more sensitive than chemical analysis to assess the removal of organic micropollutants by reverse osmosis, followed by UV/H₂O₂ treatment, as many individual compounds fell below the quantification limit of chemical analysis, yet still contributed to the observed mixture toxicity. Nonetheless in several cases, the responses in the bioassays were also below their quantification limits and therefore only three bioassays were evaluated here, representing nonspecific toxicity and two specific end points for estrogenicity and photosynthesis inhibition. Chemical analytical techniques were able to quantify 32 pesticides, 62 PCPPs, and 12 EDCs in reverse osmosis concentrate. However, these chemicals could explain only 1% of the nonspecific toxicity in the Microtox assay in the reverse osmosis concentrate and 0.0025% in the treated water. Likewise only 1% of the estrogenic effect in the E-SCREEN could be explained by the quantified EDCs after reverse osmosis. In comparison, >50% of the estrogenic effect can typically be explained in sewage. Herbicidal activity could be fully explained by chemical analysis as the sampling period coincided with an illegal discharge and two herbicides dominated the mixture effect. The mass balance of the reverse osmosis process matched theoretical expectations for both chemical analysis and bioanalytical tools. Overall the investigated treatment train removed >97% estrogenicity, >99% herbicidal activity, and >96% baseline toxicity, confirming the suitability of the treatment train for polishing water for indirect potable reuse. The product water was indistinguishable from local tap water in all three bioassays. This study demonstrates the suitability and robustness of passive sampling linked with bioanalytical tools for semicontinuous monitoring of advanced water treatment with respect to micropollutant removal.

Saxitoxin (STX) contaminates seafood and freshwater catchments worldwide. Conjugation of STX with biotin would enable new biochemical methods to quantitate STX and its analogues as well as diversify its utility as a research tool. We conjugated biotin at the region of the toxin normally occupied by a carbamoyl and this conjugate could concurrently bind both avidin/streptavidin and saxiphilin. Increasing the length of the linker between biotin and the STX portion of the semisynthetic analogue increased potency of saxiphilin binding of the STX moiety.

We report for the first time, the presence of saxitoxin (STX) in a common cephalopod, Octopus (Abdopus) sp. 5, collected from Cooke Point on the northern coastline of Western Australia. Sodium channel and saxiphilin based radio-receptor assays detected saxitoxin-like binding in octopi extracts. Further analysis by liquid chromatography-fluorescence detection (LC-FLD) identified STX as the major contributing toxin in these samples. The presence of STX was confirmed by LC-mass spectrometry and comparison of fragmentation patterns with an authentic STX standard. LC-FLD quantitation and conversion of the Octopus sp. 5 extracts revealed toxin concentrations as high as 246 microg STX/100g tissue, more than three times the US, European and Australian regulatory limit for human consumption of shellfish of 80 microg STX/100g tissue. There was no evidence of tetrodotoxin or other paralytic shellfish toxin derivatives. This level and distribution of STX in octopi poses a potential public health risk, particularly when routine toxin screening of wild catch is not regulated.

Benthic dinoflagellates of the genus Prorocentrum are common in tropical and subtropical water and several species produce phycotoxins potentially involved in human toxic outbreaks. The toxic dinoflagellate Prorocentrum borbonicum collected at La Réunion Island (France) was cultured in laboratory. A crude extract of the organism displayed significant toxicity in mice characterized by progressive limb paralysis, severe dyspnea, and death, and the toxicity was retained, after partition, in the extract's butanol-soluble fraction (BSF). Electrophysiological experiments characterizing the fraction's effect on isolated vertebrate neuromuscular preparations revealed that it depolarizes the muscle membrane and reduces the driving force for endplate potentials (EPPs) evoked by nerve stimulation, blocking directly- and indirectly-elicited muscle twitches. The depolarization induced by P. borbonicum BSF was not due to Na(+) influx through voltage-dependent Na(+) channels, since tetrodotoxin neither prevented nor suppressed the depolarization. However, ouabain, a specific ligand of the Na/K ATPase, reduced the depolarization. These results suggest the presence of palytoxin-like compounds in the fraction. HPLC-MS and MS/MS analysis showed the presence of several toxins having identical UV absorbance, among which two new isomeric toxins, borbotoxin-A and -B, of molecular mass of 1037.6 Da were isolated. The purified borbotoxin-A, had no effect on the resting membrane potential of muscle fibers and did not affect directly-elicited muscle twitches. However, the toxin reduced nerve-evoked muscle twitches, in a dose-dependent manner, reduced EPPs' amplitudes and completely blocked miniature endplate potentials. These observations suggest that the main action of borbotoxin-A is to block post-synaptic nicotinic ACh receptors.

Dioxin and pesticides with xenoestrogenic activity are environmental contaminants that are suspected of promoting human diseases such as cancers. However, few studies have addressed the molecular consequences of a combination of these contaminants, a situation that is likely to occur in the environment. We investigated the effects of natural and xenoestrogens on basal and 2,3,7,8-tetrachlorodibenzo-p-dioxin-induced cytochrome P450 (CYP) 1A1 and 1B1. The CYP1B1/1A1 ratio is a critical determinant of the metabolism and toxicity of estradiol in mammary cells. Here we show that in MCF-7 cells, 17beta-estradiol and alpha-endosulfan can repress whole cell ethoxyresorufin-O-deethylase activity, lowering CYP1A1 mRNA levels as well as promoter activity as assessed by transient transfection assays. These negative effects are observed at both the basal and tetrachlorodibenzo-p-dioxin-induced levels. Under the same conditions, CYP1B1 mRNA levels and promoter activity are not affected. The effects on mRNA-induced levels are also observed in another mammary cell line, T47D, but not in mammary cell lines that do not express aryl hydrocarbon receptor and estrogen receptor (ER). Moreover, the use of ER antagonists shows that these effects are ER dependent in MCF-7 cells. In human hepatoma HepG2 cells, which lack functional ER, alpha-endosulfan, but not 17beta-estradiol, displays a repressive effect on CYP1A1 through a different mechanism. These results show that xenoestrogens, by altering the ratio of CYP1B1/CYP1A1, could redirect estradiol metabolism in a more toxic pathway in the breast cell line MCF-7.