Special edition – Florida Everglades – Concentration of trace metals in sediments and soils from protected lands in south Florida: background levels and risk evaluation

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Article courtesy of Joffre E. Castro, Adolfo M. Fernandez, Valentina Gonzalez-Caccia, & Piero R. Gardinali | 16 April 2012 | Springer Science+Business Media Dordrecht | Shared as educational material only

Environmental Monitoring and Assessment

An International Journal Devoted to Progress in the Use of Monitoring Data in Assessing Environmental Risks to Man and the Environment© Springer Science+Business Media Dordrecht 201310.1007/s10661-012-3027-9
Joffre E. Castro-1, Adolfo M. Fernandez-2, Valentina Gonzalez-Caccia-2 and Piero R. Gardinali-2, 3
(1) Everglades National Park, South Florida Ecosystem Office, Homestead, FL 33030, USA
(2) Southeast Environmental Research Center, Florida International University, Miami, FL 33199, USA
(3) Department of Chemistry & Biochemistry, Florida International University, Miami, FL 33199, USA
Piero R. Gardinali
Received: 16 April 2012│Accepted: 27 November 2012│Published online: 4 January 2013 │Licensed permission for use by Save the Water™ #3062550211402

To read entire report: Download PDF (797kb)


A comprehensive environmental evaluation was completed on 20 metals: two reference metals (Fe, Al) and several minor trace metals (As, Ba, Co, Cr, Cu, Mn, Ni, Pb, V, and Zn) for surface soils and sediments collected from 50 sites in Everglades National Park (ENP), the coastal fringes of Biscayne National Park (BNP), and Big Cypress National Preserve. Samples were prepared by acid digestion (EPA3050) and analyzed by ICP/MS detection (EPA6020).

Although no widespread contamination was detected across the two parks and one preserve, there were some specific areas where metal concentrations exceeded Florida’s ecological thresholds, suggesting that some metals were of concern. A screening-level evaluation based on a proposed effect index grouped trace metals by their potential for causing negligible, possible, and probable effects on the biota. For example, Cu in BNP and Cr and Pb in ENP were considered of concern because their adverse effect likelihood to biota was assessed as probable; consequently, these trace metals were selected for further risk characterization.

Also, stations were ranked based on a proposed overall contamination index that showed that: site BB10 in BNP and sites E3 and E5 in ENP had the highest scores. The first site was located in a marina in BNP, and the other two sites were along the eastern boundary of ENP adjacent to current or former agricultural lands. An assessment tool for south Florida protected lands was developed for evaluating impacts from on-going Everglades restoration projects and to assist State and Federal agencies with resource management.

The tool consists of enrichment plots and statistically derived background concentrations based on soil/sediment data collected from the two national parks and one preserve. Finally, an equally accurate but much simplified approach is offered for developing enrichment plots for other environmental settings.


The Florida Everglades is one of the largest freshwater marshes in the world. A century ago, it encompassed more than 10,000 km2 (4,000 mi2), extending 160 km (100 miles) in length from Lake Okeechobee to Florida Bay and 64 km (40 miles) in width from the eastern Coastal Pineland Ridge to the western Flatwoods. This extensive freshwater ecosystem comprises wet prairies, sawgrass marshes, cypress and mangrove forests, and coastal lagoons and bays, which provide a mosaic of wildlife habitats. Early Florida settlers recognized the farming potential of peat-rich marshland in the northern Everglades and tried unsuccessfully to drain them by digging drainage canals. These early canals altered the natural drainage system and exacerbated south Florida’s droughts and flooding problems, especially during the devastating hurricanes of the 1920s and 1940s. In the late 1940s, the federal government developed a major water control project to provide water supply and flood protection for south Florida. This project helped to spur an unprecedented urban and agricultural growth in south Florida, and like the early drainage efforts, this project substantially changed the hydrology and ecology of the Everglades. Currently, one half of the historic Everglades has been lost to agriculture and urban areas; nearly three fourths of the water that flowed through Everglades has been lost to tide, and the quality of the remaining water is often degraded; and the upper three fourths of the historic Everglades system has been compartmentalized by levees and canals. These changes have caused significant losses of natural habitat that have been manifested in a 90–95 % decline in wading bird populations and also a decline in fishery resources in estuaries and bays (U.S. Army Corps of Engineers (USACE) 1999). The federal government and the state of Florida, in an unprecedented effort of cooperation, drafted a plan known as “The Comprehensive Everglades Restoration Plan (CERP),” which was approved by the United States Congress in the Water Resources Development Act of 2000, to restore, protect, and preserve the natural resources of central and southern Florida. The CERP includes 60+ key projects that will be implemented in the next 30 years at an estimated cost (2004) of $10.9 billion dollars (National Research Council (NRC) 2008). A key element of CERP is to recover natural patterns of water quantity and quality and their timing and distribution characteristics (U.S. Army Corps of Engineers (USACE) 2003). To properly assess benefits from these projects, baseline hydrologic, biogeochemical, and ecological conditions of the Everglades ecosystem first must be established. While trace metals are ubiquitous in the environment and some are essential micronutrients, all are toxic to biota above some threshold concentration. Trace metals are introduced into the environment by weathering of rocks and from anthropogenic sources. In the Everglades, urban and agricultural runoff is mostly responsible for the degradation of water and soil/sediment quality (Anderson and Flaig 1995; Goodman et al. 1999; Walker 1999; Miller et al. 2004; Fulton et al. 2004; Li et al. 2011). Trace metal water concentrations in the Everglades ecosystems, although very low and often below thresholds and method detection levels (MDLs) (Miller et al. 2004; Shinde 2007; Arroyo et al. 2009), could concentrate to elevated and toxic levels as they partition to sediments and soils under anoxic conditions. These low trace-metal water concentrations provide a false perception suggesting that impacts on the ecosystems are either nonexistent or small and negligible. A closer analysis suggests otherwise. In the Everglades, for example, mercury contamination of the biota has been extensively documented (Axelrad et al. 2010), yet mercury in surface water samples has seldom exceeded the State’s Class III standard in a decade-long monitoring of inflow structures (Rumbold 2005; Rumbold et al. 2006; Gabriel et al. 20082009). Soil/sediment concentrations appear to be better indicators of anthropogenic pollution and ecosystem contamination than water concentrations, especially when soil/sediment concentrations are normalized to reference elements from non-anthropogenic sources (Schropp and Windom 1988; Windom et al. 1989; Schropp et al. 1990; Carvalho et al. 2002).

The purposes of this study were to conduct a screening level evaluation of potential trace metal contamination in protected federal parklands in south Florida, to identify areas and metals of concern, and to develop a management tool for distinguishing natural, and yet regional, background concentrations from other low level anthropogenic-derived inputs that may increase the local trace metal storage in soils and sediments.

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Materials and methods

Study area

Everglades National Park (ENP) is located at the south end of the Florida peninsula and is characterized by a low, flat, wet plain covered by a wide grassy river with alternating ridges and sloughs, covering an area of 6,110 km2 (2,400 mi2). Biscayne National Park (BNP) is located at the southern end of Biscayne Bay and a few miles east of ENP. The park covers an area of 700 km2 (270 mi2) of which 95 % is water.

Biscayne Bay is mainly a shallow saltwater lagoon where salinity is controlled by point releases of freshwater from canals and groundwater discharges. Big Cypress National Preserve (BICY) is located northwest of ENP and BNP—and about 72 km (45 miles) west of Miami. The preserve is dominated by a wet cypress forest that supports numerous and varied habitats covering an area of 2,900 km2 (1,100 mi2). All three units are adjacent to or in close proximity to large metropolitan areas and subject to heavily managed water regimes (Fig. 1).

Sample collection and analysis

Both soil and sediment samples were collected at 28 stations in ENP, 9 stations in BICY, 11 stations in BNP, and 2 in other special interest areas outside the parks (OTH; Fig. 1) in 2006 and 2007. Surface soils/sediment samples were collected from shallow marsh areas, 30 to 100 cm deep, using a 6.25-cm-diameter, 50-cm-long acrylic coring tube. Samplers were pushed into soft soils/sediments and recovered by capping the top to create a slight vacuum.

Water was carefully drained from the top of the core, and only the top 10 cm of undisturbed soils/sediments was retained for analysis. Estuarine and canal sediments, or samples deeper than 100 cm, were collected with a 22.9-cm (9-inch) Eckman dredge. A clean Teflon or plastic spatula was used to remove the undisturbed material from the center of the dredge to prevent contamination. At each site, a total of five cores/casts collected within a 20-m (65.6 ft) radius were taken and combined into a composite sample.

Station locations and ancillary bulk sediment parameters are listed in Table 1. Samples were stored in pre-cleaned 125-ml polypropylene containers which were pre-rinsed with 10 % trace metal grade hydrochloric acid and double-deionized water. All samples were chilled at the collection site and kept at or below 4 °C after collection and during transport. Additional samples were collected for analysis of ancillary parameters. Upon arrival to the laboratory, samples were frozen at or below −10 °C until the time of analysis.

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Table 1

Site descriptors, locations, and ancillary parameters describing bulk soil/sediment characteristics

Station Latitude (N) Longitude (W) Area % TC % IC % OC
C111-1 25.2850 −80.5700 C111 Basin 14.35 11.55 2.80
C111-2 25.2860 −80.5097 C111 Basin 15.38 11.87 3.51
C111-3 25.2900 −80.4520 C111 Basin 14.81 10.98 3.83
C111-4 25.2700 −80.4430 C111 Basin 12.61 0.48 12.13
E1 25.6430 −80.5770 East boundary 13.69 3.55 10.14
E2 25.7310 −80.5770 East boundary 41.16 3.39 37.76
E3 25.5790 −80.5750 East boundary 16.75 6.18 10.57
E4 25.5460 −80.5750 East boundary 17.01 7.53 9.48
E5 25.4990 −80.5750 East boundary 15.58 5.37 10.21
E6 25.4630 −80.5900 East boundary 13.58 11.72 1.86
E7 25.4180 −80.5890 East boundary 14.05 11.44 2.61
FB1 25.2164 −80.5354 Florida Bay 12.02 8.21 3.81
FB2 25.2600 −80.4260 Florida Bay 13.80 9.13 4.67
SRS1 25.6890 −80.6350 Shark River Slough 24.64 9.81 14.84
SRS2 25.6350 −80.6550 Shark River Slough 25.37 1.15 24.22
SRS3 25.5510 −80.7850 Shark River Slough 45.41 1.97 43.44
SRS4 25.4150 −80.9630 Shark River Slough 21.83 5.08 16.75
S178 25.4084 −80.5237 Lower C-111 Basin 14.19 10.46 3.73
S18C 25.3300 −80.5250 Lower C-111 Basin 12.43 10.58 1.85
TT1 25.7400 −80.4980 Tamiami Trail 15.92 11.46 4.46
TT2 25.7530 −80.5530 Tamiami Trail 18.78 9.96 8.83
TT3 25.7620 −80.6820 Tamiami Trail 20.05 7.22 12.83
TT4 25.7610 −80.8210 Tamiami Trail 14.74 7.16 7.58
TS1 25.4021 −80.6070 Taylor Slough 15.85 10.62 5.23
TS2 25.3220 −80.6440 Taylor Slough 43.02 NA NA
TS3 25.2570 −80.6670 Taylor Slough 16.87 11.22 5.65
TS4 25.1905 −80.6400 Taylor Slough 13.37 9.06 4.31
WB1 25.4420 −80.7840 Southwest boundary 16.02 11.69 4.32
WB2 25.2470 −80.8960 Southwest boundary 17.19 6.67 10.52
WB3 25.3420 −80.9020 Southwest boundary 34.83 1.15 33.67
BICY1 26.0450 −81.3000 Big Cypress 13.73 9.64 4.09
BICY2 26.1850 −81.2670 Big Cypress 8.19 0.15 8.04
BICY3 26.1920 −81.0860 Big Cypress 7.03 0.17 6.86
BICY4 25.9580 −81.1030 Big Cypress 14.62 0.20 14.42
BICY5 25.7880 −81.1000 Big Cypress 10.88 0.13 10.75
BICY6 25.7612 −80.9360 Big Cypress 11.34 0.53 10.80
BICY7 25.6880 −80.9200 Big Cypress 14.66 10.16 4.51
BICY8 25.9191 −80.8387 Big Cypress 40.59 2.34 38.25
BICY9 26.2310 −80.9150 Big Cypress 1.12 0.34 0.78
BB1 25.5350 −80.3250 Biscayne Bay 12.91 8.49 4.43
BB2 25.5260 −80.3320 Biscayne Bay 11.96 7.99 3.97
BB3 25.5200 −80.3300 Biscayne Bay 13.18 8.88 4.29
BB4 25.5080 −80.3334 Biscayne Bay 9.11 4.46 4.65
BB5 25.4880 −80.3400 Biscayne Bay 9.70 5.15 4.55
BB6 25.5050 −80.3380 Biscayne Bay 11.22 5.57 5.65
BB7 25.4686 −80.3400 Biscayne Bay 15.42 4.25 11.17
BB8 25.4800 −80.3450 Biscayne Bay 13.63 11.09 2.54
BB9 25.4740 −80.3470 Biscayne Bay 14.69 10.83 3.87
BB10 25.4630 −80.3420 Biscayne Bay 14.58 8.80 5.78
BB11 25.4510 −80.3340 Biscayne Bay 11.65 3.52 8.13
BB12 25.5190 −80.3470 Biscayne Bay 13.64 11.21 2.43
BB13 25.6110 −80.3060 Biscayne Bay 11.76 8.14 3.62
BB14 25.5840 −80.3070 Biscayne Bay 12.67 3.33 9.34
BB15 25.5650 −80.3060 Biscayne Bay 5.97 1.24 4.73
BB16 25.5470 −80.3120 Biscayne Bay 2.36 0.22 2.14
%TC percent total carbon, %IC inorganic carbon, %OC organic carbon

Top of page [/toggle]Precautions were taken to minimize possible metal contamination throughout all sampling and analytical procedures. Bottles and material used for collection and analysis were cleaned and immersed for at least 1 week in a soap solution, 2 % Micro-90 (International Products Corporation, NJ, USA); during the second week, they were immersed in a 10 % HCl solution, rinsed with ultrapure water (Milli-Q), dried in a clean laminar flowing bench (Class 100), and stored in zip-lock bags. All reagents and containers were tested to assess for the potential introduction of contaminants during sampling and analytical laboratory procedures.

Only Optima-grade acids were used to prepare samples and standards. Procedural blanks and QA/QC samples were analyzed in each sample batch to assess precision (duplicates) and accuracy (fortified blanks and/or standard reference materials).
Soil/sediment samples were defrosted in the laboratory and air dried for up to 2 days in a plastic desiccator and kept under a clean laminar flow hood (Class 100). Dry samples (∼0.2 g) were digested in a hot block at 95 °C with concentrated nitric acid (Optima-grade, Fisher Scientific A509-212) and hydrogen peroxide (Optima-grade, Fisher Scientific P-17-0500), following an adaptation of EPA method 3050B. Samples were processed in duplicate, and a strict QA/QC protocol was followed, which included: blanks, blank spikes (LBS), matrix spikes, and reference material. Recoveries for QC samples were: blanks <3 MDL, LBS ±15 %, matrix spikes and reference material ±30 %, and duplicates < 20 % RPD.
Concentrations of 20 metals (Ag, Al, As, Ba, Be, Cd, Co, Cr, Cu, Fe, Hg, Mn, Mo, Ni, Pb, Sb, Se, Sn, V, and Zn) were determined directly or by using a sample dilution by ICP-MS (nebulization method) on a Agilent 4500A ICP-MS system. Three levels of sample dilution were necessary: 5 times for trace metals (most analytes), 10 times for minor elements (Ba, Cu, Mn, and Zn), and 1,000 times for major elements (Al and Fe). Bismuth (Bi), Ge, and In were used as internal standards. Because in most samples concentrations of several trace metals (Ag, Be, Cd, Hg, Mo, Sb, and Sn) were extremely low or below detection limits, they were excluded from the analyses. Selenium (Se) was also excluded from analysis because of potential isobaric interferences. The analyses and results of this study are based on As, Cr, Cu, Ni, Pb, and Zn, which are of potential concern in south Florida (MacDonald 1994; MacDonald et al. 2003). In addition, a selected group of metals (Al, Ba, Co, Fe, Mn, and V) were also included in the study because of their biogeochemical implications or their use as reference elements.
Carbon content was measured in duplicate using a LECO CN 2000 analyzer. Two subsamples of 100 mg were used to determine the total carbon percentage (%TC) after combustion at 1,050 °C. Another two subsamples of 100 mg were digested with HCl in a LECO CC 100 digester, and the resulting CO2 was measured by the same LECO CN 2000 analyzer to estimate the inorganic carbon content (%IC). The difference between the %TC and the %IC was the organic carbon (%OC). The calcium carbonate percentage was estimated by multiplying the %IC by a conversion factor equal to 8.33.

Effect and contamination indices (EI and CI)

License Number 3062550211402
License date Jan 05, 2013
Licensed content publisher Springer
Licensed content publication Environmental Monitoring and Assessment
Licensed content title Concentration of trace metals in sediments and soils from protected lands in south Florida: background levels and risk evaluation
Licensed content author Joffre E. Castro
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