Nitric oxide (NO) inhibits platelet function and plays a key role in the regulation of cardiovascular homeostasis. Essential hypertension is characterized by an increased risk of thrombus formation, and by an inhibition of intraplatelet NO bioactivity. We have previously shown that membrane transport of L-arginine is a rate-limiting step for plateletderived NO synthesis. This study examined the effects of exercise on the platelet L-arginine-NO pathway and aggregation and systemic inflammation markers in 13 sedentary hypertensive patients subjected to 60 min of training activity (exercise group), predominantly aerobic, three times a week for a period of 12 weeks. Six sedentary hypertensive patients participated in the control group.After 12 weeks, L-arginine transport was significantly increased and associated with increased platelet NO synthase activity and cGMP levels and reduced platelet aggregation. Moreover, exercise training reduced plasma concentrations of fibrinogen and C-reactive protein and blood pressure. The control group did not change their previous intraplatelet L-arginine-NO results and systemic inflammatory markers levels. Thus, exercise training reduces inflammatory responses, restores NO synthesis in platelets and thereby contributes to the beneficial effects of exercise in hypertension. The present study adds exercise as a new tool to reduce morbidity and mortality associated with platelet activation in hypertension.

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1. An increase in plasma concentrations of endogenous L-arginine analogues, which are inhibitors of nitric oxide (NO) synthesis, may be involved in platelet activation and the increased risk of thrombosis in essential hypertension. Nitric oxide is synthesised in platelets from the amino acid L-arginine by inducible and constitutive isoforms of NO synthase (NOS), which leads to increased levels of cGMP. 2. In the present study, we investigated basal intraplatelet cGMP levels, platelet aggregation and pro-inflammatory biomarkers in hypertensive patients. The effects of endogenous (N(G)-monomethyl-L-arginine (L-NMMA) and asymmetric dimethylarginine (ADMA); both at 1 mmol/L) and exogenous (aminoguanidine and N(G)-nitro-L-arginine; both at 1 mmol/L) L-arginine analogues and the neutral amino acid L-leucine (1 mmol/L) in inhibiting NOS activity in platelets were also investigated. 3. Twelve healthy controls and 18 hypertensive patients participated in the study. Platelet aggregation induced by collagen was increased in hypertensive patients (95 +/- 5%) compared with controls (72 +/- 5%). Basal NOS activity and intraplatelet cGMP levels were reduced in hypertensive platelets. Moreover, ADMA, L-NMMA and L-leucine were effective inhibitors of NO synthesis in both hypertensive and control platelets. Essential hypertension led to an inflammatory response, with increased plasma concentrations of fibrinogen, C-reactive protein and cytokines. 4. These findings provide evidence that, in essential arterial hypertension, the enhanced plasma levels of endogenous L-arginine analogues ADMA and L-NMMA, potent inhibitors of L-arginine transport and NO synthesis in platelets, may play a role in increased platelet aggregation via a cGMP-dependent mechanism.

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Selenium (Se) is an essential micronutrient with a narrow essentiality-toxicity range known to bioaccumulate in aquatic food webs. Selenium uptake and trophic transfer at the base of aquatic food chains represent a great source of uncertainty for Se risk assessment. The goal of the present study was to investigate Se distribution in water and sediment and its subsequent transfer into the periphyton-benthic macroinvertebrate (BMI) food chain in boreal lakes downstream from a Saskatchewan uranium mill. In particular, the present study aimed to assess potential differences in Se bioaccumulation patterns by BMI taxa to contribute to the current knowledge gap. During summer 2018 and 2019, water, sediment, periphyton, and BMI were sampled at two sites in Vulture Lake, seven sites in McClean Lake east basin, and one reference site in McClean Lake west basin. Periphyton and BMI taxa were sampled with artificial substrates (Hester-Dendy) deployed for 5 weeks in 2018 and 7 weeks in 2019; BMI were sorted into the lowest practical achievable taxonomic level and analyzed for total Se concentrations. At the diluted effluent exposure sites, Se concentrations in BMI ranged from 1.3 to 18.0 µg/g dry weight and from 0.3 to 49.3 µg/g dry weight in 2018 and 2019, respectively, whereas concentrations ranged from 0.01 to 3.5 µg/g dry weight at the reference site. Selenium concentrations in periphyton and some BMI taxa sampled near the effluent diffuser (Se < 1 µg/L) reached levels comparable to higher effluent exposure sites (Se > 2 µg/L). Despite differences in Se bioaccumulation among BMI taxa, an approximately one-to-one trophic transfer ratio was observed for benthic primary consumers and benthic predatory taxa.

There is an increasing trend in the use of real-time sensor technology to remotely monitor aquatic ecosystems. Commercially available probes, however, are currently not able to measure aqueous selenium (Se) concentrations. Because of the well-described bioaccumulation potential and associated toxicity of Se in oviparous vertebrates, it is crucial to monitor Se concentrations at sites receiving continuous effluent Se input. This study aimed to estimate Se concentrations in a boreal lake (McClean Lake) downstream from a Saskatchewan uranium mill using real-time electrical conductivity (EC) data measured by autonomous sensors. Additionally, this study aimed to derive a site-specific total aqueous Se (TSe) threshold based on Se concentrations in periphyton and benthic macroinvertebrates sampled from the same lake. To characterize effluent distribution within the lake, eight Smart Water (Libelium) sensor units were programmed to report EC and temperature for five and seven consecutive weeks in 2018 and 2019, respectively. In parallel, periphyton and benthic macroinvertebrates were sampled with Hester-Dendy's artificial substrate samplers (n = 4) at the same sites and subsequently analyzed for Se concentrations. Electrical conductivity was measured with a handheld field meter for sensor data validation and adjusted to the median lake water temperature (13 °C) registered for the deployment periods. Results demonstrated good accuracy of sensor readings relative to handheld field meter readings and the successful use of real-time EC in estimating TSe exposure (r = 0.87; r 2 = 0.84). Linear regression equations derived for Se in detritivores versus Se in periphyton and Se in periphyton versus sensor-estimated TSe were used to estimate a site-specific TSe threshold of 0.7 µg/L (±0.2). Moreover, mean Se concentrations in periphyton (16.7 ± 4.4 µg/g dry weight [d.w.]) and benthic detritivores (6.0 ± 0.4 µg/g d.w.) from one of the exposure sites helped identify an area with potential for high Se bioaccumulation and toxicity in aquatic organisms in McClean Lake.

To assess the ecological risk resulting from an accidental gasoline spill upstream from a wetland, groundwater and sediment sampling was carried out during two campaigns at the 48th and 52nd months after the spill had occurred. In total, 21 groundwater monitoring wells in the affected area were sampled plus an additional reference well located upstream from the accident location. Seven sediment sampling points were selected inside the wetland, plus a reference point upstream from the accident. Physicochemical parameters, BTEX (benzene, toluene, ethylbenzene, m-xylene, p-xylene and o-xylene) and metal concentrations were analysed to estimate the chemical risk. Acute (Allivibrio fischeri, Daphnia similis, Hyalella azteca) and chronic (Artemia salina and Desmodesmus subspicatus) toxicity assays were performed with groundwater and sediments elutriate to determine the ecotoxicological risk. Results from groundwater indicated an extreme chemical level of risk in14 out of 21 monitoring wells. These 14 wells also exhibited free-phase gasoline and lead (Pb) concentrations above the threshold values adopted by this study. The presence of Pb, however, could not be associated with the gasoline accident. High acute and chronic toxicities were reported for the majority of wells. Conversely, the risks associated with the sediments were considered low in most sampling points, and the ecotoxicity found could not be related to the presence of gasoline. Groundwater flow modelling results have evidenced the migration of the contamination plume towards the wetland. Thus, to prevent contamination from reaching the protected area, more effective groundwater clean-up techniques are still required.

Selenium (Se) bioaccumulation and toxicity in aquatic vertebrates have been thoroughly investigated over the past two decades. Limited information is available on Se bioaccumulation at the base of aquatic food webs. In this study, we selected two laboratory-reared benthic macroinvertebrates (BMI), Hyalella azteca and Chironomus dilutus, to investigate Se bioaccumulation potential in a Canadian boreal lake (McClean Lake) receiving continuous Se input from a Saskatchewan uranium mill. Laboratory and in-situ experiments were conducted in summer 2019 to assess the potential effects of biological competition on Se uptake and transfer in co-exposed H. azteca and C. dilutus. In 2021, additional experiments were included to examine the use of lab-reared H. azteca as an indicator of on-site Se exposure (native population vs lab-reared) and the major source of Se (surface water, top 1 cm and top 2-3 cm sediment layers) contributing to Se bioaccumulation in H. azteca. Except for one site (9), comparable Se bioaccumulation and trophic transfer factors (TTFs) were observed in co-exposed H. azteca (whole-body Se 0.9 to 3.1 µg /g d.w; TTFs 0.6 to 6.3) and C. dilutus (whole-body Se at 0.7 to 3.2 µg Se/g d.w.; TTFs 0.7 to 3.4). Similar non-linear dietary Se uptake and bioaccumulation were observed between lab-reared and native H. azteca (NLR, p=0.003; 4.1 ± 0.8 µg Se/g d.w) until day 14 of the experiment. Results from this study corroborate the importance of the sediment-detrital pathway relative to waterborne Se exposure, with the former leading to greater Se bioaccumulation potential to higher trophic levels via BMI.