Algal toxins and reverse osmosis desalination operations: Laboratory bench testing and field monitoring of domoic acid, saxitoxin, brevetoxin and okadaic acid

Algal toxins in Alaskan seabirds: Evaluating the role of saxitoxin and domoic acid in a large-scale die-off of Common Murres

Prevalence of algal toxins in Alaskan marine mammals foraging in a changing arctic and subarctic environment

Domoic acid and saxitoxin in seabirds in the United States between 2007 and 2018

Marine algal toxins and their vectors in southern California cetaceans

With a reverse osmosis (RO) desalination plant designed to satisfy only the contracted-for water supply, the water company would be missing out on potential benefits that could have been obtained selling water in periods of high demand. On the other hand, sizing the RO desalination plant to produce water to satisfy peak demand means incurring additional costs as well as having the plant partially idle during periods of average or low demand. A model was developed using Excel macros to perform dynamic programming to optimize the capacity expansion of an RO desalination plant. The objective function is to maximize the present value of the total net benefits over the lifetime of the RO desalination plant. The model can be used to test different scenarios to capture time-variant tourism demand and price uncertainties on investment decisions. This study focuses on tourism dominated arid coastal regions, using Sharm El Sheikh (Sharm) in South Sinai, Egypt, as an example.19 RO plants in Sharm were surveyed and data were collected including unit production costs, O&M costs, energy consumption rates, contracted-for water supply, and utilization. Unit production cost of an RO desalination plant varies according to the degree of operation of the plant. This fact has to be taken into consideration when calculating the costs of RO desalination and when deciding on the plant capacity in order to maximize the total net benefit. Using the collected data, cost functions were developed for O&M costs as a function of utilization and plant capacity. The cost model calculated similar values to the actual total net benefit for one of the surveyed RO plant taken as an example. Using the optimization model, the maximum total net benefit is obtained with a smaller installed capacity than the actual case. A modified pricing structure is suggested in the paper that ties the water selling price to consumption in an effort to reduce demand in excess of contracted-for water supply aiding the water company to fulfill its contractual commitments to all users. However, price elasticity has to be taken into consideration to determine the impact of price change on water demand.

Domoic acid (DA), a potent neurotoxin produced primarily by the diatom genus Pseudo-nitzschia, is generated during harmful algal blooms—rapid surges in toxic algae populations that result from increases in nutrient availability, temperature, and sunlight, among other environmental changes. Previously, scientists assumed that once the blooms dissipated, DA was released into and diluted within the upper ocean layer. But a study published in the April 2009 issue of Nature Geoscience shows that DA can be trapped inside the silica shells of Pseudo-nitzschia and carried to the ocean floor. Concentrations of DA in particles collected in deep oceans were several times higher than the regulatory limit set by the U.S. Environmental Protection Agency (EPA) to prevent human poisoning. DA can cause a condition called amnesic shellfish poisoning in people who eat contaminated crabs, oysters, clams, mussels, scallops, anchovies, and sardines—all of which feed on Pseudo-nitzschia. Symptoms include gastrointestinal upset, headache, dizziness, cardiac arrhythmia, coma, potential loss of short−term memory, and possibly death. Water−soluble DA concentrates in the stomachs of shellfish and tiny fish. To ingest DA, people must eat the whole organism, including the stomach, says Stephen Bates, phytoplankton scientist emeritus with Fisheries and Oceans Canada. Although elderly people are considered the most vulnerable to the effects of DA, early−life exposures also may be problematic. Recent rodent studies by biologists at the University of Prince Edward Island, published in the 23 March and 16 April 2009 issues of Physiology & Behavior, found that neonatal exposure to low doses of DA was associated with lasting cognitive deficits and behavioral problems in adult animals. Moreover, findings reported in the December 2008 issue of Marine Drugs suggest DA may be immunotoxic in mice. For the current study, researchers set up sediment traps off the coast of Southern California, where Pseudo-nitzschia blooms and DA poisoning are prevalent. The traps floated above the sea floor at depths of 540, 550, and 800 m. Sediment collected in traps set at 550 m contained up to 50 μg DA/g dry sediment, and traps set at 800 m contained up to 163 μg DA/g of dry sediment. Measurements showed that DA sank rapidly, settling to 800 m in about three days. Bates says shellfish and sediment levels are not directly comparable because the former reflects wet weight, whereas the latter reflects dry weight, but that a rough comparison can be made for the purpose of assessing relative amounts. The findings suggest that marine creatures living in deeper waters may be contaminated with DA, yet health officials currently monitor only shellfish that live close to the surface. The U.S. EPA and the Canadian Food Inspection Agency regularly check commercial shellfish beds, with increased testing during algal blooms, closing the beds when levels reach 20 μg DA/g tissue. However, says study leader Claudia Benitez−Nelson, a geochemist at the University of South Carolina, “We no longer can use algal blooms as an indicator of [potential] DA poisoning.” The fact that DA sinks to deeper waters may, in fact, help explain past mysterious outbreaks of shellfish poisoning. For instance, in 1995 lucrative deep−sea scallop beds were closed to harvesting off the coast of Nova Scotia in the Gulf of Maine. The scallops contained up to 3,400 μg DA/g tissue. “We didn’t know where the DA came from,” Bates says. “But the new data suggest that the cause could have been DA sinking down from surface blooms of Pseudo-nitzschia.” The key to curbing DA poisoning is to understand why and when Pseudo-nitzschia blooms occur. Although harmful algal blooms are mainly viewed as natural phenomena, the magnitude and occurrence of some toxic species can be exacerbated by nutrient inputs from human sewage and fertilizer and possibly other forms of coastal pollution. “People are working hard to reduce runoff from crops and lawns, but it takes time,” says Benitez−Nelson. Meanwhile, she adds, “Once [Pseudo-nitzschia] bloom, it’s very difficult to control the toxins they produce.”

Temperature dependent sensitivity of the harpacticoid copepod Nitokra spinipes to marine algal toxins

Modeling, control, and dynamic performance analysis of a reverse osmosis desalination plant integrated within hybrid energy systems

Despite a long-documented history of severe harmful algal blooms (HABs) in New England coastal waters, corresponding HAB-associated marine mammal mortality events in this region are far less frequent or severe relative to other regions where HABs are common. This long-term survey of the HAB toxins saxitoxin (STX) and domoic acid (DA) demonstrates significant and widespread exposure of these toxins in New England marine mammals, across multiple geographic, temporal and taxonomic groups. Overall, 19% of the 458 animals tested positive for one or more toxins, with 15% and 7% testing positive for STX and DA, respectively. 74% of the 23 different species analyzed demonstrated evidence of toxin exposure. STX was most prevalent in Maine coastal waters, most frequently detected in common dolphins (Delphinus delphis), and most often detected during July and October. DA was most prevalent in animals sampled in offshore locations and in bycaught animals, and most frequently detected in mysticetes, with humpback whales (Megaptera novaeangliae) testing positive at the highest rates. Feces and urine appeared to be the sample matrices most useful for determining the presence of toxins in an exposed animal, with feces samples having the highest concentrations of STX or DA. No relationship was found between the bloom season of toxin-producing phytoplankton and toxin detection rates, however STX was more likely to be present in July and October. No relationship between marine mammal dietary preference and frequency of toxin detection was observed. These findings are an important part of a framework for assessing future marine mammal morbidity and mortality events, as well as monitoring ecosystem health using marine mammals as sentinel organisms for predicting coastal ocean changes.

A theoretical analysis on upgrading desalination plants with low-salt-rejection reverse osmosis

Capital cost estimation of RO plants: GCC countries versus southern Europe

Harmful algal blooms in Chinese waters have caused serious domoic acid (DA) contamination in shellfish. Although shellfish are at particular risk of dietary exposure to DA, there have been no systematic DA risk assessments in Chinese coastal waters. A total of 451 shellfish samples were collected from March to November 2020. The presence of DA and four of its isomers were detected using liquid chromatography-tandem mass spectrometry. The spatial-temporal distribution of DA occurrence and its potential health risks were examined. DA was detected in 198 shellfish samples (43.90%), with a maximum level of 942.86 μg/kg. DA was recorded in all 14 shellfish species tested and Pacific oysters (Crassostrea gigas) showed the highest average DA concentration (82.36 μg/kg). The DA concentrations in shellfish showed distinct spatial-temporal variations, with significantly higher levels of occurrence in autumn than in summer and spring (p < 0.01), and particularly high occurrence in Guangdong and Fujian Provinces. The detection rates and maximum concentrations of the four DA isomers were low. While C. gigas from Guangdong Province in September showed the highest levels of DA contamination, the risk to human consumers was low. This study improves our understanding of the potential risk of shellfish exposure to DA-residues.

Sentinel species such as bottlenose dolphins (Tursiops truncatus) can be impacted by large-scale mortality events due to exposure to marine algal toxins. In the Sarasota Bay region (Gulf of Mexico, Florida, USA), the bottlenose dolphin population is frequently exposed to harmful algal blooms (HABs) of Karenia brevis and the neurotoxic brevetoxins (PbTx; BTX) produced by this dinoflagellate. Live dolphins sampled during capture-release health assessments performed in this region tested positive for two HAB toxins; brevetoxin and domoic acid (DA). Over a ten-year study period (2000–2009) we have determined that bottlenose dolphins are exposed to brevetoxin and/or DA on a nearly annual basis (i.e., DA: 2004, 2005, 2006, 2008, 2009; brevetoxin: 2000, 2004, 2005, 2008, 2009) with 36% of all animals testing positive for brevetoxin (n = 118) and 53% positive for DA (n = 83) with several individuals (14%) testing positive for both neurotoxins in at least one tissue/fluid. To date there have been no previously published reports of DA in southwestern Florida marine mammals, however the May 2008 health assessment coincided with a Pseudo-nitzschia pseudodelicatissima bloom that was the likely source of DA observed in seawater and live dolphin samples. Concurrently, both DA and brevetoxin were observed in common prey fish. Although no Pseudo-nitzschia bloom was identified the following year, DA was identified in seawater, fish, sediment, snails, and dolphins. DA concentrations in feces were positively correlated with hematologic parameters including an increase in total white blood cell (p = 0.001) and eosinophil (p<0.001) counts. Our findings demonstrate that dolphins within Sarasota Bay are commonly exposed to two algal toxins, and provide the impetus to further explore the potential long-term impacts on bottlenose dolphin health.

Thermodynamic analysis of a solar thermal facilitated membrane seawater desalination process

Laboratory desalination experiments with some algal toxins