In flux: Annual transport and deposition of suspended heavy metals and trace elements in the urbanised, tropical Red River Delta, Vietnam

Roberts, Lucy R.; Do, Nga T.; Panizzo, Virginia N.; Taylor, Sarah; Watts, Michael; Hamilton, Elliot; McGowan, Suzanne; Trinh, Duc A.; Leng, Melanie J.; Salgado, Jorge

Abstract

Due to the depositional environment, river deltas are said to act as filters and sinks for pollutants. However, many deltas are also densely populated and rapidly urbanizing, creating new and increased sources of pollutants. These sources pose the risk of tipping these environments from pollution sinks to sources, to the world's oceans. We provide detailed seasonal and annual assessments of metal contaminants in riverine suspended particulate matter (SPM) across the densely populated Red River Delta (RRD), Vietnam. The global contributions of elements from the RRD are all <0.2% with many elemental fluxes <0.01%, suggesting the RRD is not a major source of elemental pollution to the ocean. However, ‘hotspots’ of metal pollution due to human activity and the impacts of tropical storm Son Tinh (July 2018) exceed both national level regulations and international measures of toxicity (e.g. enrichment factors). There is widespread ‘extreme pollution’ of Cd (enrichment factor >40) and concentrations of As higher than national regulation limits (>17 mg/Kg) at all sites other than one upstream, agricultural-dominated tributary in the dry season. These ‘hotspots’ are characterised by high inputs of organic matter (e.g. manure fertiliser and urban wastewater), which influences elemental mobility in the particulate and dissolved phases, and are potentially significant sources of pollution downstream. In addition, in the marine and fresh water mixing zone, salinity effects metal complexation with organic matter increasing metals in the particulate phase. Our calculations indicate that the delta is currently acting as a pollutant sink (as determined by high levels of pollutant deposition ∼50%). However, increased in-washing of pollutants and future projected increases in monsoon intensity, saline intrusion, and human activity could shift the delta to become a source of toxic metals. We show the importance of monitoring environmental parameters (primarily dissolved organic matter and salinity) in the RRD to assess the risk of transport and accumulation of toxic metals in the delta sediments, which can lead to net-increases in anthropogenic pollution in the coastal zone and the incorporation of toxic elements in the food chain.

Citation

Roberts, L. R., Do, N. T., Panizzo, V. N., Taylor, S., Watts, M., Hamilton, E., McGowan, S., Trinh, D. A., Leng, M. J., & Salgado, J. (2022). In flux: Annual transport and deposition of suspended heavy metals and trace elements in the urbanised, tropical Red River Delta, Vietnam. Water Research, 224, Article 119053. https://doi.org/10.1016/j.watres.2022.119053

• Journal Article Type: Article
• Acceptance Date: Sep 2, 2022
• Online Publication Date: Sep 8, 2022
• Publication Date: Oct 1, 2022
• Deposit Date: Sep 9, 2022
• Publicly Available Date: Sep 9, 2022
• Journal: Water Research
• Print ISSN: 0043-1354
• Electronic ISSN: 1879-2448
• Publisher: Elsevier
• Peer Reviewed: Peer Reviewed
• Volume: 224
• Article Number: 119053
• DOI: https://doi.org/10.1016/j.watres.2022.119053
• Keywords: Pollution; Waste Management and Disposal; Water Science and Technology; Ecological Modeling; Environmental Engineering; Civil and Structural Engineering
• Public URL: https://nottingham-repository.worktribe.com/output/10919223
• Publisher URL: https://www.sciencedirect.com/science/article/pii/S004313542200999X
• Additional Information: This article is maintained by: Elsevier; Article Title: In flux: Annual transport and deposition of suspended heavy metals and trace elements in the urbanised, tropical Red River Delta, Vietnam; Journal Title: Water Research; CrossRef DOI link to publisher maintained version: https://doi.org/10.1016/j.watres.2022.119053; Content Type: article; Copyright: © 2022 The Author(s). Published by Elsevier Ltd.