Speciation of heavy metals in recent sediments of three coastal ecosystems in the Gulf of Cadiz, Southwest Iberian Peninsula

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  • 2833

    Environmental Toxicology and Chemistry, Vol. 22, No. 12, pp. 28332839, 2003q 2003 SETAC

    Printed in the USA0730-7268/03 $12.00 1 .00

    Environmental Chemistry

    SPECIATION OF HEAVY METALS IN RECENT SEDIMENTS OF THREE COASTALECOSYSTEMS IN THE GULF OF CA DIZ, SOUTHWEST IBERIAN PENINSULA

    VERONICA SA ENZ, JULIA N BLASCO,* and ABELARDO GO MEZ-PARRADepartmento de Oceanografa, Instituto de Ciencias Marinas de Andaluca (C.S.I.C.), Campus Universitario de Ro San Pedro,

    11510 Puerto Real, Cadiz, SpainDepartmento de Qumica-Fsica, Facultad de Ciencias del Mar de Universitario de Cadiz, Campus Universidad de Ro San Pedro s/n,

    11510 Puerto Real, Cadiz, Spain

    (Received 23 September 2002; Accepted 10 March 2003)

    AbstractA five-step sequential extraction technique was used to determine the partitioning of Cr, Mn, Fe, Cu, Zn, Cd, and Pbamong the operative sedimentary phases (exchangeable ions, carbonates, manganese and iron oxides, sulfides and organic matter,and residual minerals) in coastal sediment from three locations in the southwest Iberian Peninsula. Two sites are located close toindustrial areas, the salt marshes of the Odiel River and Bay of Cadiz, and one in a nonindustrial area, the Barbate River saltmarshes. The Odiel River salt marshes also receive the drainage from mining activities in the Huelva region. In the sediments fromthe Bay of Cadiz and Barbate River salt marshes, Cr, Cu, Fe, and Zn were extracted from the residual fraction at percentages higherthan 60%. In the sediments from the Odiel River salt marshes, concentrations of all the metals, except Cu, Zn, and Cd, exceeded60% in the residual fraction as well. In the sediments from the Bay of Cadiz and Barbate River salt marshes, the main bioavailablemetals were Mn and Cd; in those from the Odiel River salt marshes, the main bioavailable metals were Zn and Cd, respectively.The environmental risk was determined by employing the environmental risk factor (ERF), defined as ERF 5 (CSQV 2 Ci/CSQV),where Ci is the heavy metal concentration in the first four fractions and CSQV is concentration sediment quality value (the highestconcentration with no associated biological effect). Our results showed that the sediments from the Cadiz Bay and Barbate Riversalt marshes do not constitute any environmental risk under the current natural conditions. In contrast, in the Odiel River saltmarshes, Cu, Zn, and Pb yielded ERFs of less than zero at several sampling stations and, consequently, pose a potential threat forthe organisms in the area. This is a consequence of the high levels of metals in the area derived from the mining activity (pyrite)and industrial activities and the association of these heavy metals with more labile fractions of the sediments.

    KeywordsSpeciation Sediment Heavy metals Salt marshes

    INTRODUCTIONThroughout history, estuaries have been favored sites for

    human settlements and their associated industrial activities andhave therefore received heavy contaminant inputs. Estuarinesediments show a strong tendency to accumulate contaminants,especially heavy metals; thus, analysis of these sediments con-stitutes a rapid means of obtaining time-integrated informationconcerning a range of sedimentological variables [1]. In ad-dition, estuaries often include wetland sites of internationallyrecognized ecological importance as well as economic im-portance for their shellfish production. Heavy metals are eco-logically relevant, mainly because of their toxicity and theirnonbiodegradable character [2].

    Sediments act as sinks for trace metals; thus, they becomea more or less permanent part of the ecosystem. Remobilizationprocesses reintroduce them into the ecosystem in bioavailableforms [3]. Metals can be released into the water phase whenconditions such as pH, redox potential, ionic strength, and theconcentration of organic complexing agents are appropriate;therefore, sediments also act as sources of the metals [4].

    The biogeochemical and ecotoxicological significance of agiven element is determined not only by its concentration ina natural or terrestrial system but also by its chemical form,which in turn is controlled by the physical, chemical, andbiological characteristics of that system [5]. Knowledge re-garding the chemical speciation of heavy metals in sediments

    * To whom correspondence may be addressed(julian.blasco@icman.csic.es).

    is important for assessing the capacity of those sediments toact as sources of the potentially toxic metals. The determi-nation of the total concentrations of metals is not, on its own,sufficient for prediction of such behavior [6].

    Currently, the methods used most frequently to study thedistribution of metals in a solid phase are based on partitiontechniques using different chemical extractants in sequence(i.e., the use of selective chemical extraction is widespread)[714]. It is generally recognized that the partitioning of tracemetals achieved by such procedures is operational, and theresults are determined by several experimental factors, suchas the nature of the reagents used, time, temperature, mixingrates, the ratio of reagent to sediment, and the physicochemicalcharacteristics of the sample (especially its chemical compo-sition). The chemical composition of a sample could causeheterogeneous chemical reactions, leading to changes in thedistribution of metals during extraction, such as the precipi-tation of newly formed compounds and readsorption of re-leased metals [1521].

    Speciation is very useful, not only for determining the de-gree of association of the metals to the sediments and the extentto which they might be remobilized into the environment butalso for differentiating metals with a lithogenic origin fromthose with an anthropogenic origin [22]. Metals associatedwith any of the following four fractionsthe adsorptive orexchangeable fraction, the carbonate fraction, the reduciblefraction, and the organic fractionare considered to be moremobile and, therefore, more easily released from the sediment

  • 2834 Environ. Toxicol. Chem. 22, 2003 V. Saenz et al.

    Fig. 1. Map of the Odiel River salt marshes (AG), Cadiz Bay (CB),and Barbate River (BR) salt marshes (Andalucia, southwest IberianPeninsula). Locations of sampling stations are shown.

    Table 1. Granulometric distribution and organic carbon (OC) and total carbon (TC) in the three sampling ecosystemsa

    Odiel River salt marshes

    A B C D E F G CB BR

    % Clay% Silt% Sand% OC% TC

    8.5341.5149.96

    1.971.52

    9.1737.6353.20

    1.291.12

    13.0476.6210.34

    2.692.17

    18.5769.0112.42

    2.732.04

    11.3635.4053.24

    1.671.15

    1.100.83

    98.070.340.19

    4.198.24

    87.571.140.33

    5.1124.8370.06

    1.653.07

    16.7649.4733.77

    1.712.37

    a Sampling stations (AG) are located in the Odiel River salt marshes (Huelva, Spain) and Bay of Cadiz (CB) and Barbate River (BR) in CadizBay and Barbate River salt marshes (Cadiz, Spain).

    and potentially more dangerous. These four fractions covermetals from anthropogenic sources and, therefore, give infor-mation regarding the type and severity of the pollution to whicha particular environment has been exposed. Metals reportingto the inert fraction may be interpreted as having originatedfrom geochemical or natural sources (i.e., of lithogenic origin)[3].

    In the present study, we investigated the partitioning ofseven metals (Cr, Mn, Fe, Cu, Zn, Cd, and Pb) among differentfractions in superficial sediments from three coastal areas inthe southwest (SW) Iberian Peninsula: The salt marshes of theOdiel River (OR), the Bay of Cadiz (CB), and the Barbate

    River (BR). All three areas are of considerable ecological rel-evance, and the aim of this work is to provide informationconcerning the distributions of heavy metals in the sedimentssampled in these three valuable ecosystems to predict the en-vironmental risks associated with these metals.

    MATERIALS AND METHODS

    Study areaThe salt marshes of the OR, CB, and BR are located on

    the SW coast of the Iberian Peninsula (Fig. 1). The OR wasdeclared a biosphere reserve because of its large populationof migratory birds. The CB hosts a wide diversity of aquaticspecies, and many areas have been transformed for the de-velopment of aquaculture activities [23]. (It is also catalogedas a nature park.) The BR is also cataloged as a nature parkand has commercial activities of bivalve cultivation (mainlyshellfish and oysters). Despite their status as administrativelyprotected areas, these zones are exposed to different types andlevels of contamination. The OR marshes are affected by inputsof contaminants from the Huelva industrial area and the ORitself, which flows through a well-known mining area calledthe Iberian Pyrite Belt. The CB includes an international portwith heavy maritime traffic and for decades has supported amajor industrial activity in the marine construction sector; inrecent years, this industrial activity has been diversified by theincorporation of other industries using metals, such as themanufacture of vehicle and aircraft components. The BR is anarea relatively free from domestic and industrial contaminants,and its pollution inputs are derived more from agriculturalactivities. Therefore, it is included in the present study as areference against which the zones subjected to metal pollutioncan be evaluated.

    Sampling and sample pretreatmentSediments were collected from June through July 1996 from

    nine sampling stations: A, B, C, D, E, F, and G in the OR(zone 1), CB, (zone 2), and BR (zone 3). Their locations areshown in Figure 1. A Van Veen grab was used to collectapproximately 1 kg of superficial sediment (05 cm) at eachof the sampling points. Samples were transferred to polyeth-ylene bags and stored under a N2 atmosphere at 248C. Aportion