RESUMO
BACKGROUND: Environmental DNA (eDNA) is the DNA that can be extracted from an environmental sample, enabling the monitoring of whole biological communities across a large number of samples, at a potentially lower cost, which can significantly benefit river conservation. A systematic mapping protocol was designed to investigate the use of eDNA in rivers, specifically in terms of research topics, geographic and taxonomic biases, as well as information gaps. Furthermore, the potential research opportunities of eDNA in rivers and possible paths to find this kind of information on available platforms are identified. METHODS: A published systematic map protocol was applied, consisting of a search for published articles and gray literature in two bibliographic databases and one search engine. All search results were submitted to a 2-stage screening for relevance and pertinence in accordance with pre-defined eligibility criteria. Data extraction and codification regarding country of study, year, taxonomic group, sequencing platform, and type of technique employed resulted in a publicly available database. RESULTS: From 7372 studies initially obtained by the search, 545 met the inclusion criteria spanning a period from 2003 to 2022. The five countries with most studies are: USA (134), Japan (61), China (54), Brazil (29) and the UK (25). The most used fragments to analyze DNA are 16S and COI, whilst 26S and 23S are the least used. Only 84 (15%) of the studies reported hypervariable regions, among which the most used are V4 and V5. Regarding taxonomic groups, fishes are most often studied (176), followed by bacteria (138) and virus (52), while fungi is the least studied group (3). Concerning data availability, 229 (42%) studies provided access to sequencing data. CONCLUSIONS: This study presents a comprehensive analysis of the available evidence regarding the implementation of the eDNA methods in rivers. The findings indicate that since the year 2003, this approach has been applied to aquatic lotic systems, and their recent increase can be attributed to the development of Next-Generation-Sequencing technologies and their reduced costs. However, there is a bias towards high-income countries, particularly USA and Europe. Widespread use and applications of this approach at a global level would allow for the generation of a large amount of information that can be compared between countries to understand if responses of aquatic systems follow similar patterns worldwide.
RESUMO
The present work evaluated the effects of (i) feeding a water contaminated with 80 mg/L PCE to bioreactors seeded with inoculum not acclimated to PCE, (ii) coupling ZVI side filters to bioreactors, and (iii) working in different biological regimes, i.e., simultaneous methanogenic aeration and simultaneous methanogenic-denitrifying regimes, on fluidized bed bioreactor performance. Simultaneous electron acceptors refer to the simultaneous presence of two compounds operating as final electron acceptors in the biological respiratory chain (e.g., use of either O2 or NO3- in combination with a methanogenic environment) in a bioreactor or environmental niche. Four lab-scale, mesophilic, fluidized bed bioreactors (bioreactors) were implemented. Two bioreactors were operated as simultaneous methanogenic-denitrifying (MD) units, whereas the other two were operated in partially aerated methanogenic (PAM) mode. In the first period, all bioreactors received a wastewater with 1 g chemical oxygen demand of methanol per liter (COD-methanol/L). In a second period, all the bioreactors received the wastewater plus 80 mg perchloroethylene (PCE)/L; at the start of period 2, one MD and one PAM were coupled to side sand-zero valent iron filters (ZVI). All bioreactors were inoculated with a microbial consortium not acclimated to PCE. In this work, the performance of the full period 1 and the first 60 days of period 2 is reported and discussed. The COD removal efficiency and the nitrate removal efficiency of the bioreactors essentially did not change between period 1 and period 2, i.e., upon PCE addition. On the contrary, specific methanogenic activity in PAM bioreactors (both with and without coupled ZVI filter) significantly decreased. This was consistent with a sharp fall of methane productivity in those bioreactors in period 2. During period 2, PCE removals in the range 86 to 97 % were generally observed; the highest removal corresponded to PAM bioreactors along with the highest dehalogenation efficiency (94 %). Principal component analysis as well as cluster analysis confirmed the trends mentioned above, i.e., the better performance of PAM over MD, and the unexpected no effect of the ZVI side filters on PCE removal and dehalogenation efficiencies. To the best of our knowledge, this is the first report on the combined treatment ZVI-biological of a water polluted with PCE, where the biological operation relied on simultaneous electron acceptors.