Laboratory desalination experiments with some algal toxins

Abstract

Over the last several decades, countries throughout the world have experienced an escalating and worrisome trend in the incidence of harmful algal blooms (HABs). A concern is that highly potent algal toxins might be retained in the treated water, posing a threat to human health.Seawater contaminated with saxitoxins, domoic acid, okadaic acid, and brevetoxins was desalinated using small (<100 mL capacity) reverse osmosis and distillation equipment.Analyses of desalinated water samples indicated efficient removal of the four toxins to greater than 99%, except brevetoxins for which some carryover was observed during distillation.Hypochlorite concentrations of 4 ppm or higher were sufficient to react with all of the saxitoxins, domoic acid and okadaic acid in the samples that contained initial toxin concentrations up to 1,250 ng.mL -1 . Brevetoxins appeared to be unaffected in experiments in which the toxins were exposed to up to 30 ppm hypochlorite in seawater at 35 °C for 60 min. These results and their implications in terms of desalination plant design and operation are discussed. Abbreviations

Seawater reverse osmosis desalination and (harmful) algal blooms

“…Therapeutic intervention is primarily limited to symptomatic treatment and life support. (Laycock et al 2012). Acute singledose lethality of seafood toxins has been extensively studied, but chronic and/or repeated exposure to low toxin concentrations, which might be the case with low levels of toxin in desalinated water, has not been adequately examined.…”

“…removal can be achieved with RO membranes (Laycock et al, 2012;Boerlage and Nada, 2014) or nanofiltration (e.g., Dixon et al, 2011). Given the typical molecular weight size range of marine algal toxins of 0.3-0.9 Da ( Considering the lower flux and higher operating pressure in SWRO, the direct relative impact of AOM accumulation on its operational performance is expected to be less severe compared to MF/UF systems.…”

Investigation of Algal Biotoxin Removal during SWRO Desalination through a Materials Flow Analysis

“…Most existing studies in the literature have been limited to examining removal of these marine algal toxins across RO membranes alone, concluding that the RO membranes remove a considerable portion (>99%) of dissolved algal toxins [8][9][10]16]. However, these studies were restricted to the laboratory/pilot scale of analysis and did not consider the effects of pretreatment processes on toxin removal.…”

“…In addition, the associated human health risk from consumption of desalinated water during HABs has not been fully assessed [8][9][10]16]. Preliminary risk assessments have ascertained that the risk of acute intoxication from consumption of desalinated water is rather low [8][9][10].…”

“…The increasing frequency and severity of harmful marine algal blooms (HABs), has posed a serious threat to full-scale SWRO desalination facilities operating worldwide [8][9][10]. Caron and co-workers [11] acknowledged two important impacts of HABs on desalination facilities: (1) complete removal of algal toxins; (2) increased demand on pretreatment for membrane fouling prevention.…”