Posts Tagged 'toxicity'

Implications of pH manipulation methods for metal toxicity: not all acidic environments are created equal

The toxicity of many metals is impacted by environmental pH, through both competition and complexation by hydroxide and carbonate ions. To establish safe environmental regulation it is important to properly define the relationship between pH and metal toxicity, a process that involves manipulating the pH of test water in the lab. The current study compares the effects of the three most common pH manipulation methods (carbon dioxide, acid-base addition, and chemical buffers) on acute Pb toxicity of a model fish species, Pimephales promelas. Acidification of test water revealed that the Pb and Pb2+ LC50 values were impacted by the pH manipulation method, with the following order of effects: HCl < CO2 < MOPS. Conversely no differences in toxicity were observed when test pH was alkalinized using MOPS or NaOH. The different impacts of pH manipulation methods on Pb toxicity are likely due to different physiological stresses resulting from the respective methods; the physiological implications of each method are discussed. The results suggest that when studying the impacts of pH on metal toxicity it is important to properly replicate the ambient conditions of interest as artificial buffering using CO2 environments or organic buffers significantly affects the physiology of the test organisms above and beyond what is expected from pH alone. Thus, using CO2 and organic buffers overestimates the impact of acid pH on Pb toxicity.

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Global change and the future of harmful algal blooms in the ocean

The frequency and intensity of harmful algal blooms (HABs) and phytoplankton community shifts toward toxic species have increased worldwide. Although most research has focused on eutrophication as the cause of this trend, many other global- and regional-scale anthropogenic influences may also play a role. Ocean acidification (high pCO2/low pH), greenhouse warming, shifts in nutrient availability, ratios, and speciation, changing exposure to solar irradiance, and altered salinity all have the potential to profoundly affect the growth and toxicity of these phytoplankton. Except for ocean acidification, the effects of these individual factors on harmful algae have been studied extensively. In this review, we summarize our understanding of the influence of each of these single factors on the physiological properties of important marine HAB groups. We then examine the much more limited literature on how rising CO2 together with these other concurrent environmental changes may affect these organisms, including what is possibly the most critical property of many species: toxin production. New work with several diatom and dinoflagellate species suggests that ocean acidification combined with nutrient limitation or temperature changes may dramatically increase the toxicity of some harmful groups. This observation underscores the need for more in-depth consideration of poorly understood interactions between multiple global change variables on HAB physiology and ecology. A key limitation of global change experiments is that they typically span only a few algal generations, making it difficult to predict whether they reflect likely future decadal- or century-scale trends. We conclude by calling for thoughtfully designed experiments and observations that include adequate consideration of complex multivariate interactive effects on the long-term responses of HABs to a rapidly changing future marine environment.

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Ocean acidification increases the toxicity of contaminated sediments

Ocean acidification (OA) may alter the behaviour of sediment-bound metals, modifying their bioavailability and thus toxicity. We provide the first experimental test of this hypothesis with the amphipod Corophium volutator. Amphipods were exposed to two test sediments, one with relatively high metals concentrations (Σmetals 239 mg kg−1) and a reference sediment with lower contamination (Σmetals 82 mg kg−1) under conditions that mimic current and projected conditions of OA (390 to 1140 μatm pCO2). Survival and DNA damage was measured in the amphipods, while the flux of labile metals was measured in the sediment and water column using Diffusive Gradients in Thin-films. The contaminated sediments became more acutely toxic to C. volutator under elevated pCO2 (1140 μatm). There was also a 2.7-fold increase in DNA damage in amphipods exposed to the contaminated sediment at 750 μatm pCO2, as well as increased DNA-damage in organisms exposed to the reference sediment, but only at 1140 μatm pCO2. The projected pCO2 concentrations increased the flux of nickel (Ni) and zinc (Zn) to labile states in the water column and pore water. However, the increase in metal flux at elevated pCO2 was equal between the reference and contaminated sediments or, occasionally, greater from reference sediments. Hence, the toxicological interaction between OA and contaminants could not be explained by effects of pH on metal speciation. We propose that the additive physiological effects of OA and contaminants will be more important than changes in metal speciation in determining the responses of benthos to contaminated sediments under OA. Our data demonstrate clear potential for near-future OA to increase the susceptibility of benthic ecosystems to contaminants. Environmental policy should consider contaminants within the context of changing environmental conditions. Specifically, sediment metals guidelines may need to be re-evaluated to afford appropriate environmental protection under future conditions of OA.

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High CO2 and silicate limitation synergistically increase the toxicity of Pseudo-nitzschia fraudulenta

Anthropogenic CO2 is progressively acidifying the ocean, but the responses of harmful algal bloom species that produce toxins that can bioaccumulate remain virtually unknown. The neurotoxin domoic acid is produced by the globally-distributed diatom genus Pseudo-nitzschia. This toxin is responsible for amnesic shellfish poisoning, which can result in illness or death in humans and regularly causes mass mortalities of marine mammals and birds. Domoic acid production by Pseudo-nitzschia cells is known to be regulated by nutrient availability, but potential interactions with increasing seawater CO2 concentrations are poorly understood. Here we present experiments measuring domoic acid production by acclimatized cultures of Pseudo-nitzschia fraudulenta that demonstrate a strong synergism between projected future CO2 levels (765 ppm) and silicate-limited growth, which greatly increases cellular toxicity relative to growth under modern atmospheric (360 ppm) or pre-industrial (200 ppm) CO2 conditions. Cellular Si:C ratios decrease with increasing CO2, in a trend opposite to that seen for domoic acid production. The coastal California upwelling system where this species was isolated currently exhibits rapidly increasing levels of anthropogenic acidification, as well as widespread episodic silicate limitation of diatom growth. Our results suggest that the current ecosystem and human health impacts of toxic Pseudo-nitzschia blooms could be greatly exacerbated by future ocean acidification and ‘carbon fertilization’ of the coastal ocean.

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Ocean acidification in the IPCC AR5 WG II

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