Elsevier

Chemosphere

Volume 90, Issue 9, March 2013, Pages 2396-2402
Chemosphere

PBDEs and PCBs in sediments of the Thi Nai Lagoon (Central Vietnam) and soils from its mainland

https://doi.org/10.1016/j.chemosphere.2012.10.067Get rights and content

Abstract

Concentration and distribution of PCBs, PCB 11, and PBDEs in both surficial sediment and soil samples, taken from a zone subject to recent accelerated development, were investigated to assess the environmental quality and understand both natural and anthropogenic processes that influence contaminant behaviors. Values of PCB and PBDE are in the lower range of those reported in literature, typical of low impacted coastal zones. This could be due to efficient processes of resuspension and removal. Contaminants in the lagoon showed higher concentrations in sediments from sites close to the city and the outfalls of the industrial area, while soils showed maximum values in the northern samples. In addition, congener patterns and statistical analyses suggest the presence of effective degradation processes, especially for PBDEs, with the exception of the most concentrated samples that may indicate a direct input. PCB 11 is a significant component (up to 18%) in most lagoon sediments. Its presence is strongly associated with fine particles, thus the distribution seems to be driven mainly by the system hydrodynamic and does not trace the sources. Due to evaporation, only flooded agricultural soils show a similar relative abundance of this congener.

Highlights

► Levels and patterns of PCBs, PCB 11, and PBDEs in surface sediments and soils. ► Main natural and anthropogenic processes in tropical areas are changing rapidly. ► Key processes are identified by salinity, porosity and grain size patterns. ► PCBs, PCB 11 and PBDEs levels are similar to those found far from direct sources. ► Efficacy of degradation processes are confirmed by congener patterns and statistics.

Introduction

Halogenated organic chemicals have been widely used for a variety of purposes since the beginning of the 20th century, and their industrial production has been widespread for commercial purposes (Alaee et al., 2003). PCBs and PBDEs are two groups of organic chemical substances, both forming a family of 209 congeners.

PCBs, commercially produced mainly as Aroclors, had a myriad of applications (Hu and Hornbuckle, 2010). Their toxicity was confirmed in the 1970s, and therefore their use in open systems has been forbidden ever since. However, they remain a current concern because they are still present in closed systems or stored in landfills, and can be reintroduced in the environment by evaporation and leakage (Bhavsar et al., 2004). Moreover, second-hand items (goods produced before the ban as coolants and lubricants in transformers and capacitors, hydraulic and heat exchange fluids, and so on) are widespread through the black market in Asian regions (Wong et al., 2007). The congener PCB 11 (3,3′-dichlorobiphenyl) is absent or present at very low concentration in original commercial Aroclor mixtures (Hu and Hornbuckle, 2010, Rodenburg et al., 2010), and its production from degradation is not likely (Rhee et al., 1993). However, PCB 11 has been shown to be a global contaminant (Rodenburg et al., 2010) and is measured in consumer goods mainly containing azo- and phthalocyanine pigments, including newspapers, packaging, plastic bags, and so on (Rodenburg et al., 2010).

The commercial production of PBDEs began in 1970s, as flame retardants in a variety of industrial and consumer applications (Alaee et al., 2003). The commercial products principally contain penta-, octa-, or deca-BDE mixtures (Alaee et al., 2003). Their toxicity and increasing levels in marine mammals, sediments, bird eggs and human tissues make them of environmental concern (De Wit, 2002). Such as PCBs, PBDEs are bioaccumulative, resistant to degradation, and subject to long-range transport (Wang et al., 2005). Currently, the production of penta- and octa-BDEs has been banned in the European Union (EU) and North America. Deca-BDE has also been banned from some of these countries but no restriction on PBDEs exists in Asia (Yan-Ping et al., 2010).

The information about PCB and/or PBDE sources and concentrations in Vietnam is limited to the most industrialized metropolitan areas (e.g., Ramu et al., 2007, Nguyen et al., 2010, Tuan et al., 2010) and some data are available for PCBs in coastal lagoons (Frignani et al., 2007, Giuliani et al., 2011). However, Vietnam has undergone a wide process of economic reform in 1986, which laid the foundations for a market economy, and since then, the country has experienced a high economic growth together with a boom in household food and no-food consumption (Figuié and Moustier, 2009). Then, it is likely that environmental levels of anthropogenic contaminants have increased in response to the recent rapid industrialization/economic development.

The aim of this study was to investigate PCBs, PCB 11, and PBDE concentrations and distributions in surface sediments of the Thi Nai Lagoon and in the mainland soils, improving the knowledge of main natural and anthropogenic processes active in the Lagoon, and some of its environmental characteristics.

Section snippets

Study area

Recently, the Thi Nai Lagoon (Fig. 1) has acquired a particular economic importance, because it is one of the key areas designed to drive the socioeconomic development in Central Vietnam, which completion is scheduled for 2020. The Thi Nai bridge, whose construction was completed in 2006, represents the access way to the new economic zone in the Phuong Mai peninsula. This will include tourist sites, together with industrial and residential zones and the enlargement of the commercial port with

Materials and methods

Sampling locations are shown in Fig. 1a. Sediments (TN) and soils (TS) were collected in June 2010. Soils were collected at selected sites around the border of the Lagoon, each representing an area of particular interest (Fig. 1a): a flooded rice field (TS02); a dry soil from a rice field (TS04); a cultivated field, quite close to a small village (TS05); a flooded rice field by the lagoon border, where several aquaculture ponds are located (TS06); a domestic garden, quite close to the

Sediment features

Fig. 1a shows the areal distribution of sediment porosity. Values generally increase along a N–S gradient, being lower at the western edge of the lagoon, close to artificial fish farms, and maximum in proximity of the lagoon inlet and the industrial port of Quy Nhon City. In particular the central area, north of the Thi Nai bridge, shows a patchwork distribution with zones characterized either by lower (∼0.55) or higher (∼0.65) porosities. The content of fines reflects the porosity distribution

Depositional patterns and particle origin in the Thi Nai Lagoon and surrounding soils

Porosity is defined by the complex interaction of many factors (Athy, 1930), however, the highly significant correlation (Pearson correlation coefficient) observed between fine particles’ content and porosity (r = 0.98, p < 0.01; see Tables S2 and S3 in the Supplementary material) allows to identify some key processes that influence its areal distribution. Indeed, the lagoon’s depositional pattern is dominated by the joint flow of the rivers Cai and Con, along a NW-SE gradient, the area close to

Acknowledgements

Funds for this work were provided by the Italian Ministry of Foreign Affairs – Directorate General for Cultural Cooperation and Promotion (MAE-DGCCP), the Vietnamese Ministry of Science and Technology (MOST) and the Italian scientific institutions involved in the research, in the framework of a bilateral project. The authors thank M. Brunello for his help in some analyses and N.H. Anh for his contribution to field work. This is contribution No. 1776 from the Istituto di Scienze Marine, Bologna

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