The partitioning of platinum in aquatic ecosystems and disruption to aquatic communities

Abstract

Due to the increasing presence of platinum (Pt) in the environment, it becomes crucial to identify its toxic potential in species at risk of being exposed, especially those found in aquatic environments where metal pollutants tend to accumulate. Comprehensive characterisation of possible adverse effects of Pt exposure on aquatic organisms remains vague. To accurately determine the impact on the aquatic environment, the compartmentalisation of Pt in the aquatic environment needs to be understood. However, the various environmental influencing factors and the binding characteristics of PGEs identified in recent studies concluded that laboratory studies (controlled environment) alone do not provide sufficient information concerning the behaviour of PGEs in the aquatic environment. As a result of the various environmental influencing factors, field-based studies cannot provide laboratory “controlled” information on the behaviour of PGEs as it can be tough to correlate field-based results to that of laboratory studies. Therefore, it is crucial to address the void between these two scientific approaches in the PGE study area and broaden our knowledge on the effects of Pt in the aquatic ecosystem. Using 18 microcosms, mimicked natural aquatic communities were established. These communities were then exposed to a range of standard Pt concentrations (0.1, 1,10,100, and 500 μgPt/L) for eight weeks. Samples were collected on three separate occasions: 48 hours (acute), four weeks (chronic), and eight weeks (chronic). These samples were then analysed to determine the compartmentalisation of Pt in the aquatic environment. Platinum concentrations in the different aquatic compartments (water, sediment, macrophytes, and artificial mussels) were quantified using an Atomic Absorption Spectrometer (AAS) and an Inductively Coupled Plasma-Mass Spectrometer (ICP-MS) to determine the different Pt concentrations within each of the compartments. The separate compartments were divided into bioavailable environmental accumulation (water and sediment) and bioaccumulation (macrophytes and artificial mussels). Platinum concentrations in the water column decreased over time. Similarly, the sediment, macrophytes and, artificial mussels (AM) showed higher initial accumulated Pt followed by a progressive decrease over time. Two macrophyte species were identified (Fontinalis antipytetica and Charophyta sp) and both species accumulated Pt over time. Interestingly, the accumulation levels between the two species varied, where the F. antipytetica reported a higher accumulation level than the Charophyta sp. The difference in accumulation can be explained by the different habitat preferences of the species in the ecosystem, and their differences in Pt absorption and metabolism since macrophyte species rooted in the sediment are known to be more sensitive to metal pollution than suspended macrophytes (Gupta et al., 2013).

Epiphytic and benthic diatom community assemblages were sampled 48-hours (acute) and eight weeks (chronic) after exposure to assess the impact of different Pt exposures on diatom community assemblages. Initial observations reported that diatom communities showed little to no response after the 48-hours; however, all the samples collected from the aquatic habitat indicated the presence of pollution tolerant taxa after a chronic eight-week Pt exposure. Diatom deformities were also observed, although these deformities occurred at Pt levels higher than those present in the environment. A total of 25 type 1 (morphological abnormalities of the frustule) teratologies were identified from four 500 μgPt/L chronic exposure samples. Resulting in 1.025% of teratologies identified for the epiphytic diatom community and 1.875% of teratologies for the benthic diatom community. This teratology indicates a possible disruptive potential of increased Pt concentrations on aquatic communities.