Short-term toxicity and binding of platinum to freshwater periphyton communities

Potential cellular targets of platinum in the freshwater microalgae Chlamydomonas reinhardtii and Nitzschia palea revealed by transcriptomics

Platinum group element levels have increased in natural aquatic environments in the last few decades, in particular as a consequence of the use of automobile catalytic converters on a global scale. Concentrations of Pt over tens of μg L-1 have been observed in rivers and effluents. This raises questions regarding its possible impacts on aquatic ecosystems, as Pt natural background concentrations are extremely low to undetectable. Primary producers, such as microalgae, are of great ecological importance, as they are at the base of the food web. The purpose of this work was to better understand the impact of Pt on a cellular level for freshwater unicellular algae. Two species with different characteristics, a green alga C. reinhardtii and a diatom N. palea, were studied. The bioaccumulation of Pt as well as its effect on growth were quantified. Moreover, the induction or repression factors of 16 specific genes were determined and allowed for the determination of possible intracellular effects and pathways of Pt. Both species seemed to be experiencing copper deficiency as suggested by inductions of genes linked to copper transporters. This is an indication that Pt might be internalized through the Cu(I) metabolic pathway. Moreover, Pt could possibly be excreted using an efflux pump. Other highlights include a concentration-dependent negative impact of Pt on mitochondrial metabolism for C. reinhardtii which is not observed for N. palea. These findings allowed for a better understanding of some of the possible impacts of Pt on freshwater primary producers, and also lay the foundations for the investigation of pathways for Pt entry at the base of the aquatic food web.

Implications of kinetically-hindered metals in ecotoxicological studies: Effect of platinum spike aging on its toxicity to Dunaliella salina

Platinum (Pt) is considered an emerging environmental micro-contaminant due to its increasing use in anthropogenic activities during the past decades. However, there are still important gaps in the understanding of its biogeochemical behavior in the aquatic environment - e.g. its speciation, reactivity and fate - mainly as a result of the analytical challenge of the determination of its typical ultra-trace environmental concentrations. Also, Pt is a kinetically-hindered metal displaying slow reaction kinetics, which has important implications regarding eco-toxicological studies. That is, investigation of its toxicity under laboratory-controlled conditions may therefore require ensuring that equilibrium speciation conditions are reached before starting the experiments. In order to shed further light on this issue, in this study we have monitored the speciation changes during aging of the Pt(IV) spikes in controlled media (seawater) using an UV-Vis spectrophotometry. Platinum toxicity to the green microalgae Dunaliella salina was then compared, using standardized tests, with fresh and aged Pt(IV) spikes at the mg L^-1 concentration range. Following 96-hour exposure, ecotoxicological assays consisting in spectrometric measurements of chlorophyll-a concentrations and Effective Concentrations (EC) of Pt resulting in the inhibition of 10% and 50% of algae growth rate were calculated (EC₁₀ and EC₅₀, respectively). Daily monitoring of Pt speciation reflected the transition from PtCl₆^2- (spike) to hydrolyzed species, probably in the form [PtCl_3-n(OH)_3+n]^2-, n = 0-3. Exposure experiments showed that after a short period of aging (10 days), Pt(IV) toxicity increased one order of magnitude compared to freshly spiked media. These results confirm the relevance of considering spike aging to ensure that speciation equilibrium conditions are attained in order to produce environmental realistic eco-toxicological data.

A Multimethod Approach for Investigating Algal Toxicity of Platinum Nanoparticles

The ecotoxicity of platinum nanoparticles (PtNPs) widely used in for example automotive catalytic converters, is largely unknown. This study employs various characterization techniques and toxicity end points to investigate PtNP toxicity toward the green microalgae Pseudokirchneriella subcapitata and Chlamydomonas reinhardtii. Growth rate inhibition occurred in standard ISO tests (EC₅₀ values of 15-200 mg Pt/L), but also in a double-vial setup, separating cells from PtNPs, thus demonstrating shading as an important artifact for PtNP toxicity. Negligible membrane damage, but substantial oxidative stress was detected at 0.1-80 mg Pt/L in both algal species using flow cytometry. PtNPs caused growth rate inhibition and oxidative stress in P. subcapitata, beyond what was accounted for by dissolved Pt, indicating NP-specific toxicity of PtNPs. Overall, P. subcapitata was found to be more sensitive toward PtNPs and higher body burdens were measured in this species, possibly due to a favored binding of Pt to the polysaccharide-rich cell wall of this algal species. This study highlights the importance of using multimethod approaches in nanoecotoxicological studies to elucidate toxicity mechanisms, influence of NP-interactions with media/organisms, and ultimately to identify artifacts and appropriate end points for NP-ecotoxicity testing.

Speciation of platinum in blood plasma and urine by micelle-mediated extraction and graphite furnace atomic absorption spectrometry

A highly sensitive and selective technique for the speciation of platinum by cloud point extraction prior to determination by graphite furnace atomic absorption spectrometry (GFAAS) was described. The separation of Pt(II) from Pt(IV) was performed in the presence of 4-(p-chlorophenyl)-1-(pyridin-2-yl)thiosemicarbazide (HCPTS) as chelating agent and Triton X-114 as a non-ionic surfactant. The extraction of Pt(II)-HCPTS complex needs temperature higher than the cloud point temperature of Triton X-114 and pH = 7, while Pt(IV) remains in the aqueous phase. The Pt(II) in the surfactant phase was analyzed by GFAAS, and the concentration of Pt(IV) was calculated by subtraction of Pt(II) from total platinum which was directly determined by GFAAS. The effect of pH, concentration of chelating agent, surfactant, and equilibration temperature were investigated. An enrichment factor of 42 was obtained for the preconcentration of Pt(II) with 50 mL solution. Under the optimum experimental conditions, the calibration curve was linear up to 30 μgL(-1) with detection limit of 0.08 μgL(-1) and the relative standard deviation was 1.8%. No considerable interference was observed due to the presence of coexisting anions and cations. The accuracy of the results was verified by analyzing different spiked samples (tap water, blood plasma and urine). The proposed method was applied to the speciation analysis of Pt in blood plasma and urine with satisfactory results.

Cadmium toxicity and uptake by mats of the freshwater diatom: Navicula pelliculosa (Bréb) Hilse

Contaminant uptake by algae, and its subsequent toxicity, has important ramifications for aquatic biomonitoring and environmental risk assessment. To study the effects of cadmium on diatom mats, a series of experiments was undertaken. These investigated the sensitivity of Navicula pelliculosa mats to cadmium, uptake of cadmium across a range of exposure concentrations, influence of mat biomass and thickness on uptake, and cadmium uptake by mats over time. Diatom mat formation proved to be sensitive to cadmium exposure, with a 96-h EC(50) of 31 microg/L. The rapid uptake of cadmium over 15 min was a linear function of exposure concentration and was not significantly affected by mat thickness. Cadmium uptake over time was also a linear function of exposure concentration for time periods up to 5 h. Linear uptake was likely due to the availability of algal binding sites as cadmium ions diffused through the diatom mats. Internal high-pH microenvironments may also have influenced uptake, through cadmium precipitation or enhanced adsorption within the mats. The lack of a significant relationship between mat biomass and uptake could be explained by the static water exposure conditions. Other studies have shown that cadmium uptake by algal mats was only significantly affected by biomass under flowing water conditions. Flowing water appeared to facilitate the diffusion of cadmium ions through the algal mats. Our research demonstrates the propensity of diatom mats to adsorb cadmium to achieve concentrations that could inhibit macroinvertebrate grazing. Overall, these findings contribute to a greater understanding of cadmium bioavailability in aquatic ecosystems and to the further development of benthic algae as an effective biomonitoring tool.

Impact of humic substances on the aqueous solubility, uptake and bioaccumulation of platinum, palladium and rhodium in exposure studies with Dreissena polymorpha

Zebra mussels (Dreissena polymorpha) were exposed to different types of water containing PGE salts (PtCl4, PdSO4, RhCl3) to investigate the influence of humic substances on the aqueous solubility, uptake and bioaccumulation of noble metals. The results showed a time dependent decrease of the aqueous PGE concentrations in tank water for all groups. This could mainly be related to non-biological processes. The aqueous solubility of Pd and Rh was higher in humic water compared with non-chlorinated tap water, whereas Pt showed opposing results. Highest metal uptake rates and highest bioaccumulation plateaus were found for Pd, followed by Pt and Rh. Pd uptake and bioaccumulation was significantly hampered by humic substances, whose presence appear to increase Pt uptake and bioaccumulation. No clear trend emerged for Rh. Differences in effects of humic matter among the PGE may be explained by formation of metal complexes with different fractions of humic substances.