Abstract
This study aims to investigate the effect of two different groups of phenolic compounds (the alkylphenols nonylphenol (NP) and octylphenol (OP), and the chlorophenol pentachlorophenol (PCP)) on constructed wetlands (CWs) performance, including on organic matter, nutrients and contaminants removal efficiency, and on microbial community structure in the plant bed substrate. CWs were assembled at lab scale simulating a vertical flow configuration and irrigated along eight weeks with Ribeira de Joane (an urban stream) water not doped (control) or doped with a mixture of NP and OP or with PCP (at a 100 μg·L−1 concentration each). The presence of the phenolic contaminants did not interfere in the removal of organic matter or nutrients in CWs in the long term. Removals of NP and OP were >99%, whereas PCP removals varied between 87% and 98%, mainly due to biodegradation. Microbial richness, diversity and dominance in CWs substrate were generally not affected by phenolic compounds, with only PCP decreasing diversity. Microbial community structure, however, showed that there was an adaptation of the microbial community to the presence of each contaminant, with several specialist genera being enriched following exposure. The three more abundant specialist genera were Methylotenera and Methylophilus (methylophilaceae family) and Hyphomicrobium (hyphomicrobiaceae family) when the systems were exposed to a mixture of NP and OP. When exposed to PCP, the three more abundant genera were Denitromonas (Rhodocyclaceae family), Xenococcus_PCC_7305 (Xenococcaceae family) and Rhodocyclaceae_uncultured (Rhodocyclaceae family). To increase CWs efficiency in the elimination of phenolic compounds, namely PCP which was not totally removed, strategies to stimulate (namely biostimulation) or increase (namely bioaugmentation) the presence of these bacteria should be explore. This study clearly shows the potential of vertical flow CWs for the removal of phenolic compounds, a still little explored subject, contributing to promote the use of CWs as nature-based solutions to remediate water contaminated with different families of persistent and/or emergent contaminants.
Highlights
Endocrine disrupting chemicals (EDCs) are characterized as external agents that obstruct the formation, release, transport, attachment, activity or displacement of body natural hormones regulating homeostasis, development, reproduction and behavior [1]
This study aimed to investigate the effect of two different groups of phenolic EDCs compounds on constructed wetlands (CWs) performance, including on organic matter, nutrients and contaminants removal efficiency, and on microbial community structure in the plant bed substrate, improving the knowledge regarding the processes occurring in CWs to be able to promote the implementation and good operation of these green systems
Diversity or dominance of microbial community was not affected by the presence of alkyphenolic compounds, but the presence of PCP cause a decrease in microbial community diversity
Summary
Endocrine disrupting chemicals (EDCs) are characterized as external agents that obstruct the formation, release, transport, attachment, activity or displacement of body natural hormones regulating homeostasis, development, reproduction and behavior [1]. Various synthetic chemicals with known endocrine disruption capacity have been identified Alkylphenols, such as nonylphenol (NP) and octylphenol (OP), and chlorophenols, such as pentachlorophenol (PCP), are examples of phenolic EDCs [2,3]. Due to their potential adverse effects on ecosystems and human health, these phenolic compounds were listed as a priority substance in the EU Water Framework Directive [4] and classified as persistent organic pollutants in the environment for many countries [5,6], indicating that different strategies should be develop to reduce their input into the environment. APEOs are of concern because the microbial breakdown of nonylphenol polyethoxylates (NPnEO) and octylphenol polythoxylates (OPnEO) originate NP and OP, respectively, which are more toxic than the parent compounds [2]
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