Occurrence and Contamination of Rare Earth Elements in Urban Mangroves of Shenzhen, South China

Xiaoxue Shen,Minwei Chai,Fang Yang,Ruilli Li,Ye Cao

doi:10.3390/su13052503

Abstract

Mangroves acted as sinks of terrestrial pollutants, but the occurrence and contamination of rare earth elements (REEs) in urban mangroves lacked systematic evaluation. In rapidly developing Shenzhen, China, four typical urban mangroves were selected to determine the REEs in urban mangroves, including Baguang mangrove (BGM) and Futian mangrove (FTM) featured with ecological preserve and central business district, respectively; Xixiang mangrove (XXM) and Shajing mangrove (SJM) both featured with industry district. The mean concentrations of total REEs (TREEs) in sediment (0–25 cm depth, μg g−1) were SJM (465.28) > FTM (411.25) > XXM (342.76) > BGM (118.63), with Ce to be the dominant REEs element. The depositions of REEs in urban mangroves were significantly affected by sediment sulfur accumulation and fine sediment, including silt and clay fractions. The main fractionation pattern of REEs in urban mangroves was the enrichment of light REEs (LREEs) and loss of heavy REEs (HREEs). Geo−accumulation index, modified degree of contamination, pollution load index, and potential ecological risk index showed the moderately contaminated level of REEs in FTM, followed by SJM, and XXM, with uncontaminated level in BGM. This study provided important information on REEs in urban mangroves for pollution prevention and remediation in the future.

Highlights

Rare earth elements (REEs), an element group including the lanthanide element series and yttrium, have similar physic-chemical properties and similar environmental behaviors, being extensively applied in electronic technology, medicines, agriculture, and industry around the world [1,2]
Over the past few decades, REEs have got into the soil, water, and air with increasing exploitation and utilization of REEs-related products [5,6]
Once REEs enter the environment, they could be enriched in biota and damage human health through the food chain, resulting in various environmental and health issues [4,9]

Summary

Introduction

Rare earth elements (REEs), an element group including the lanthanide element series and yttrium, have similar physic-chemical properties and similar environmental behaviors, being extensively applied in electronic technology, medicines, agriculture, and industry around the world [1,2]. In REE resource-rich China, various kinds of products related to REEs have been produced for decades in multiple fields, including industry, agriculture, forestry, and animal husbandry [3,4]. Mangrove is an important intertidal coastal system, providing a myriad of ecological services and receives lots of terrestrial pollutants [10,11]. REEs are relatively new pollutants, and provide insight into the elemental cycling in the coastal wetlands and the abundance of REEs in the source areas [12,13].

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