Development of site-specific sediment quality guidelines for North and South Atlantic littoral zones: Comparison against national and international sediment quality benchmarks
Introduction
Dredging activities can cause several negative impacts to the aquatic ecosystems, such as the elimination of benthic habitats and resuspension of nutrients and contaminants. Special concern arises on the disposal of the dredged material; the simple discharge in marine waters implies several environmental consequences, including physical disturbance (burrowing, smothering) of benthic communities [1] and chemical contamination [2].
There are different options to deal with dredged material, which include [3], [4]: (i) beneficial uses—land creation and improvement, beach nourishment, agricultural uses, wetlands restoration, creation of nesting islands, etc.; (ii) disposal in ocean or continental waters; (iii) treatment, such as the separation of sediment contaminated fractions; and (iv) discharge into confined disposal facilities. The selection of the best management option is in a great extent dependent on the quality of the dredged material. Therefore, a reliable assessment of the sediments to be dredged is needed to assure that the disposal of such material will be environmentally harmless as well as cost-effective.
Despite experts have been claiming that the use of biological testing is crucial to adequately understand the hazard posed by contaminated sediments [5], [6], [7], decision-making on the management of dredged materials commonly relies on a simple comparison between levels of contaminants measured in the sediments against national sediment quality criteria or classical sediment quality guidelines (SQGs) (e.g. effects range-low and effects range-median – ERL and ERM; threshold effect level and probable effects level – TEL and PEL).
The SQGs provide a basis to identify the concentrations of chemicals that can potentially cause adverse biological effects [8]. Nevertheless, the bulk concentrations of contaminants may not correlate well to the bioavailability [9] inasmuch as several factors affect the availability of contaminants from sediments to the biota (and consequently the toxicity), such as sediment grain size, pH, salinity, organic matter content, acid volatile sulfides (AVS) contents, among others [10], [11], [12], [13]. Consequently, national guidelines, which are intended to predict toxic effects of contaminant levels for different environments and sediment types, may not suitably address the specificities of each local and situation in national and wide geographic areas. In the other hand, sediment quality guidelines derived based on site-specific data is able to better predict the toxicity of contaminants in each specific coastal environment.
The development of the SQGs can be performed by employing different approaches, which can be divided in the two broad categories [14]: (i) mechanistically or theoretically, based on theoretical understanding of the partitioning of chemicals in the sediments and the toxicity of the dissolved contaminants in the interstitial water (e.g. equilibrium partitioning – EqP [15]); (ii) empirically based, derived from databases of concentrations of specific contaminants and their correspondence with observed biological effects (e.g. ERL and ERM [16], [17]; TEL and PEL [18]; apparent effects thresholds – AET [19]). Besides, a third approach, so-called “consensus approaches”, was developed recently with the attempt of providing a synthesis of multiple guidelines into a single SQG or a range of SQGs [14], mainly focused on polycyclic aromatic hydrocarbons [20] and polychlorinated biphenyls [21].
In Brazil, sediment quality criteria to orientate dredged material management are given by the Resolution no. 344/2004 from the National Council for the Environment – CONAMA [22]. Such values were established based on the American and Canadian SQGs [23], [24], [25]. In Spain, the document Recommendations for the management of dredged material in ports of Spain [26] proposes sediment quality guidelines based on geochemical considerations [27] and it has been applied in the characterisation of the sediments dredged in Spanish ports; however, this document does not establish statutory contaminant concentration limits.
The aim of this work was to develop site-specific SQGs through the integration of sediment physical, chemical, ecotoxicological, and macrobenthic invertebrate community data using multivariate analysis for two estuarine and port zones in Southeastern Brazil (Santos Estuarine System and Paranaguá Estuarine System) and three in Gulf of Cádiz, Southern Spain (Ría of Huelva, Bay of Cádiz, and Bay of Algeciras), and compare these values against national and traditionally used international benchmark values. The areas under study are ecologically important and they are affected by different sources of pollution, such as domestic sewage, industrial effluents, urban runoff, as well as contamination due to the port activities [5], [28], [29], [30]. The establishment of site-specific ranges of contaminants concentrations related to biological responses (ecological and toxicological) will better subsidise the management of the dredged material in the studied zones and the comparison of site-specific SQGs against general SQGs gives an insight into the adequacy of the use of national criteria or international guidelines for assessing dredged material and sediment quality in different coastal environments in South and North Atlantic. Furthermore, the use of the same method to derive SQGs for Brazilian and Spanish port zones aimed to assess the viability of application of this technique with an international scope and providing an internationally harmonised methodology for site-specific SQGs derivation.
Section snippets
Approach
In this study, site-specific sediment quality guidelines were derived for two areas in Southeastern Brazil: Santos Estuarine System (SES) and Paranaguá Estuarine System (PES) (Fig. 1a and b); and three areas in Gulf of Cádiz (GC), Southern Spain: Ría of Huelva, Bay of Cádiz, and Bay of Algeciras (Fig. 2a–c).
All areas of study present prominent port activities besides ecologically important ecosystems (especially mangroves and Atlantic Rainforest in Brazil and salt marshes in Spain). In SES,
Sediment physical–chemical characteristics, toxicity and benthic community structure data
Results of sediment physical–chemical and toxicity data are summarised in Appendix A.
Detailed description of chemical, toxicity and benthic community results were previously reported in Cesar et al. [5], Choueri et al. [28], and Abessa et al. [39]. In general for Brazilian and Spanish areas, higher sediment contamination and toxicity were found at inner parts of the estuaries as well as associated to contamination sources (urban sewage outfall, industrial areas, ports). Among GC areas, the
Discussion
As mentioned afore, two different data matrices were used to derive SQGs for SES, and consequently some contaminants’ SQGs are duplicated for this study area; namely, nickel, lead and zinc were the contaminants of concern in SES ‘a’ which are in common with SES ‘b’. There was a slight difference between the SQGs derived for these contaminants, which could be expected since the data were taken from different studies, i.e. samples were taken in different periods, different sampling methods were
Conclusions
The site-specific SQGs derived in this study were different from the sediment quality standards employed at national and international level. In general, the site-specific SQGs were more restrictive than the national guidelines applied in their respective countries as well as the classical sediment quality guideline. Thus, this finding confirms that, in some instances, the application of general SQGs may not fully address local particularities of each environment. These results underpin the
Acknowledgements
The authors express thanks to CAPES/MEC-DGU for the financial support to this research (CAPES #099/06; BEX 3238/06-7; BEX 3239/06-3; BEX2492/08-03; BEX2300/08-7; MEC-Spain PHB 2005-0100-PC). Additionally, the work was partially funded by the Spanish Ministry of Education project (CTM2005-07282-C03-C01/TECNO), FAPESP (process number 98/00808-6) and partially supported by UNITWIN/UNESCO/WiCop.
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