Lipophilic Shellfish Poisoning Toxins in Marine Invertebrates from the Galician Coast.

For the purpose of assessing human health exposure, it is necessary to characterize the toxins present in a given area and their potential impact on commercial species. The goal of this research study was: (1) to screen the prevalence and concentrations of lipophilic toxins in nine groups of marine invertebrates in the northwest Iberian Peninsula; (2) to evaluate the validity of wild mussels (Mytilus galloprovincialis) as sentinel organisms for the toxicity in non-bivalve invertebrates from the same area. The screening of multiple lipophilic toxins in 1150 samples has allowed reporting for the first time the presence of 13-desmethyl spirolide C, pinnatoxin G, okadaic acid, and dinophysistoxins 2 in a variety of non-traditional vectors. In general, these two emerging toxins showed the highest prevalence (12.5-75%) in most of the groups studied. Maximum levels for 13-desmethyl spirolide C and pinnatoxin G were found in the bivalves Magallana gigas (21 µg kg-1) and Tellina donacina (63 µg kg-1), respectively. However, mean concentrations for the bivalve group were shallow (2-6 µg kg-1). Okadaic acid and dinophysistoxin 2 with lower prevalence (1.6-44.4%) showed, on the contrary, very high concentration values in specific species of crustaceans and polychaetes (334 and 235 µg kg--1, respectively), to which special attention should be paid. Statistical data analyses showed that mussels could be considered good biological indicators for the toxicities of certain groups in a particular area, with correlations between 0.710 (for echinoderms) and 0.838 (for crustaceans). Polychaetes could be an exception, but further extensive surveys would be needed to draw definitive conclusions.

Short-Term Interactions of Noctiluca scintillans with the Toxic Dinoflagellates Dinophysis acuminata and Alexandrium minutum: Growth, Toxins and Allelopathic Effects.

The Galician Rías (NW Iberian Peninsula) are an important shellfish aquaculture area periodically affected by toxic episodes often caused by dinoflagellates such as Dinophysis acuminata and Alexandrium minutum, among others. In turn, water discolorations are mostly associated with non-toxic organisms such as the heterotrophic dinoflagellate Noctiluca scintillans, a voracious non-selective predator. The objective of this work was to study the biological interactions among these dinoflagellates and their outcome in terms of survival, growth and toxins content. To that aim, short experiments (4 days) were carried out on mixed cultures with N. scintillans (20 cells mL-1) and (i) one strain of D. acuminata (50, 100 and 500 cells mL-1) and (ii) two strains of A. minutum (100, 500 and 1000 cells mL-1). Cultures of N. scintillans with two A. minutum collapsed by the end of the assays. Both D. acuminata and A. minutum exposed to N. scintillans arrested its growth, though feeding vacuoles in the latter rarely contained any prey. Toxin analyses at the end of the experiment showed an increase in intracellular OA levels in D. acuminata and a significant reduction in PSTs in both A. minutum strains. Neither OA nor PSTs were detected in N. scintillans. Overall, the present study indicated that the interactions among them were ruled by negative allelopathic effects.

Mercury interactions with algal and plastic microparticles: Comparative role as vectors of metals for the mussel, Mytilus galloprovincialis.

The adsorption and desorption of Hg onto and from microplastics (MP) and microalgae (MA) were investigated, and fitted using pseudo-first-order and pseudo-second order kinetics models. Then, the potential role of MP as vector for the entrance and accumulation of Hg (MP-Hg) in comparison to natural pathways (via MA -MA-Hg-, and dissolved -WB-Hg-) was investigated in mussel. Mussels were exposed to a single dose of Hg (2375 ng ind-1) for 4 h. Although the clearance of MP-Hg was relevant (82 %), it was lower than that of MA (95 %) and MA-Hg (94 %). The amount of the Hg accumulated and eliminated was higher in mussels exposed to MP-Hg (1417 ng Hg) than in those exposed to MA-Hg (882 ng Hg) and WB-Hg (1074 ng Hg). However, Hg accumulation was similar in the three mussel groups (≈800 ng Hg). This was related to the fast elimination of Hg still attached to MP by MP-Hg mussels. Hg was mainly accumulated in digestive gland in MA-Hg and MP-Hg mussels, and in gills in WB-Hg mussels. Overall, the results indicated that MP facilitated the entrance of Hg in mussel but also promoted Hg elimination, which could limit the toxicological risk of Hg adsorbed onto MP.

Microplastics do not affect standard ecotoxicological endpoints in marine unicellular organisms.

In this study, the acute toxicity of microplastics (MPs) on unicellular organisms as marine decomposers and microalgae was assessed, by evaluating standards endpoints included in International Standard Organization (ISO) protocols. The bacteria Vibrio fischeri and the diatom Phaeodactylum tricornutum were exposed to different sizes (1-500 µm) of polyethylene MPs in order to evaluate bioluminescence inhibition and microalgal growth. No acute toxicity was found on bacteria or microalgae in an order of magnitude above environmentally relevant concentrations, suggesting that tested MPs did not affect the investigated biological processes. In conclusion, standard ecotoxicological endpoints are not sufficiently sensitive to assess the potential effects of MPs on decomposers and primary producers, conversely to nanoplastics. These findings highlight that the current approach for MP risk assessment in unicellular species should be revised, by providing alternative endpoints to be included in standardized protocols, able to monitor the fate and biological effects of MPs.

Biodynamics of mercury in mussel tissues as a function of exposure pathway: natural vs microplastic routes.

In the marine environment, metals can be present dissolved or adsorbed to suspended particles. In the last decades a new type of particle has been introduced, microplastics (MPs). The exposure route of pollutants influences their accumulation and distribution into tissues. A pulse-chase experiment was conducted in which mussels were exposed to Hg: adsorbed onto MPs and microalgae (MA) and dissolved (WB). Mussels accumulated the same amount of Hg independently of particle, due to the Hg loading in both particles and their acceptability were similar. The highest Hg accumulation occurred in gill when the Hg exposure was through water and in digestive gland when Hg was adsorbed to particles. More than 70% of the Hg uptake through MPs was quickly eliminated due to: i) part of the cleared MPs might not really be ingested but adhered to body surfaces of mussels, ii) MPs ingested were eliminated through faeces as they are non-nutritive particles which may be rejected in stomach preventing their entry into digestive gland and iii) high affinity of Hg on surface of MPs which meant that Hg was mainly eliminated jointly to MPs. The organic nature of MA facilitates the entry of Hg into digestive gland where MA are intracellularly digested releasing the Hg adsorbed onto their surfaces. In this case, Hg may reach deeper levels by translocation of the Hg incorporated into gland towards foot and remaining tissues, a process that might occur through haemolymph. All of the Hg accumulated in WB during the exposure was internally absorbed into tissues, and later translocated from gill to gland. Although Hg elimination rate in MPs mussels was greater than in the other exposure pathways, an important amount of Hg was maintained through the depuration period, thus we cannot and should not neglect the risk of MPs as vectors for mercury.

Effect of microplastics on the toxicity of chlorpyrifos to the microalgae Isochrysis galbana, clone t-ISO.

It is highly likely that phytoplanktonic organisms will interact with MPs in the ocean, and consequently with the pollutants sorbed onto their surfaces. Microalgae play an essential role in maintaining the balance of the marine ecosystem due to the fact that they are a primary producer and the base of marine trophic chains. Therefore, their fitness represents an important index in the assessment of water quality. The objectives of this study were i) to assess the toxicity of MPs and the pesticide chlorpyrifos (CPF) to the microalgae, Isochrysis galbana, clone t-ISO and ii) to ascertain whether the presence of MPs affects the toxicity of CPF. Microalgae growth rate was selected as the endpoint and a commercial virgin PE micronized powder was chosen as a micro-plastic model, with mean size ranging from 2 to 6 µm, assayed until 25 mg L-1. CPF was tested at concentrations ranging from 0 to 4 mg L-1. A constant concentration of MPs (5 mg L-1) was loaded with increasing doses of CPF (0-3 mg L-1) with a 2 h incubation period. Bioassays were performed at 20 °C, in glass tubes of 50 ml, with air and constant light and an exposure time of 72 h. Cell counts were performed using a Coulter Counter Multisizer III and HPLC was used to quantify the partition of this pollutant among MPs and water. Although microalgae growth was not impacted by MPs, growth was clearly affected by exposure to CPF from 2 mg L-1 and above, with a total growth inhibition at concentrations over 3 mg L-1. Subsequent to incubation, 80% of CPF was sorbed onto MP surfaces. Two different dose-response curves resulted from CPF bioassays depending on the presence of MP, with lower percentages of inhibition when CPF was presented through MP. Thus, the adsorption of CPF onto MP surfaces modulates the toxicity of CPF on I. galbana growth through a reduction in its toxicity, as CPF is adsorbed onto MP surfaces which are less bio-available to the algal cells.