Metals in fish tissue from the Laguna de Pom-Atasta of Campeche, Mexico.
Resumen. -- Concentracion de metales (Ba, Cd, Co, Cu, Ni, Pb, V, Zn, Ag, Cr y Fe) en musculo de peces de la Laguna de Pom-Atast de Campeche, Mexico fueron determinados. La mayoria de los metales, excepto Ni, Zn y Fe se encontraron en niveles por debajo de las ppm (mg/kg de peso seco). Niveles altos de Cd y Pb en las muestras analizadas de los peces muestra que estas concentraciones se han observado en otras zonas del Golfo de Mexico. Sin embargo, las concentraciones de Cd y Pb se encontraron por debajo de las concentraciones de metales establecidas para peces de acuerdo a los limites establecidos por la Secretaria de Salud de Mexico.
Transfer of metals from point and nonpoint sources into coastal waters is of major interest in environmental chemistry and biology (Szefer et al. 1996; Summers et al. 1996). Heavy metals within coastal lagoons are an increasing concern; they are highly phytotoxic and can change the primary productivity of the coastal environment (Lacerda 1994). Metals, such as Zn, Fe, Cu and Mn, which are essential biological micronutrients for many aquatic organisms can become toxic at elevated concentrations (Sunda 1988; 1989). Other metals, for example Pb and Ag, are not required for growth and are highly toxic in trace amounts (Merian 1991). Therefore, knowledge about types and levels of heavy metals entering coastal lagoons is critically important.
There are relatively few studies on metal concentrations in tropical marine species. It is imperative to analyze metals within commercial species in assessing potential toxic levels from the human-nutritional standpoint (Vazquez et al. 1995; Vazquez & Sharma 1996). The Laguna de Pom-Atasta represents an important ecosystem in the southern Gulf of Mexico because of its valuable fish and wildlife resources. This study was undertaken to determine the concentrations of metals (Ba, Cd, Co, Cu, Ni, Pb, V, Zn, Ag, Cr and Fe) in fish collected from the Laguna de Pom-Atasta of Campeche, Mexico, in order to establish metal levels in fish tissue from these waters.
MATERIALS AND METHODS
The Pom-Atasta lagoon system is situated southern Gulf of Mexico and is 80 [km.sup.2] in area with a mean depth of 1.5 m. Freshwater from the San Padro-San Pablo River enters from the east into the lagoon through an artificial canal. The lagoon is also connected to the Gulf through a natural canal and Terminos lagoon (Gutierrez et al. 1982). A Mexico Petroleum gas pipeline passes through the Pom-Atasta lagoon (Fig. 1).
The mean annual air temperature of the area is 27.2[degrees]C. The region experiences three climatic changes during the year: a dry season from February to May, and two rainy seasons, from June to September and October to January. The heavy rain in the later season is caused by winter storms, Nortes and strong N and NW winds (30 mph). Surface water temperatures and salinities range from 23.1-25.4[degrees]C and 34.2-36.1 ppt, respectively.
Fish samples were collected during three sampling events (October 1996, November 1996 and January 1997) from five stations in the Laguna de Pom of Campeche, Mexico (Fig. 1). The dredging activities at the gas pipeline (close to station 4, Fig. 1) occurred in November 1996. A sampling period comprised before, during and after dredging activities. The five stations were selected based on water flow, dredging activities, and closeness to the Gulf of Mexico. After collection of fish, species identified included Eugerres plumieri, Bagre marinus, Mugil curema, Centropomus undecimalis and Cyprinus carpus. The size of specimens varied from 10-18 cm. Fish samples were not enough at station 2 and 5 in January 1997 to perform analysis.
Approximately 20 individuals of mixed species were randomly taken and were immediately ice-frozen and brought to the laboratory for analysis. In the laboratory, fish were dissected to obtain muscle samples. The muscle samples were dried to constant weights at 55[degrees]C. Homogenization and pulverization of composite samples of fish muscle were achieved in a teflon mortar. A 0.5 g powder of each muscle sample of the muscle was put into a digestion vessel and 5 mL of HN[O.sub.3], 1 mL of HCl and 10 mL of deionized water were added to the vessel to carry out digestion. The digestion of metal in samples was done in the microwave (MDS-2000 CEM) for 30 minutes. After digestion, samples were diluted to 25 mL before determining metal concentration in samples using the atomic absorption technique.
[FIGURE 1 OMITTED]
Metal concentrations were determined on a Perkin Elmer model 2380 with a graphite furnace model MGA400. Standard solutions were prepared by dissolving metals in 1:1 solutions of nitric and hydrochloric acids. Certified tuna fish homogenate was obtained from the International Laboratory of Marine Radioactivity Mosee Oceanography, Inc. MC 98000, Monaco and was analyzed for metal contents using the same digestion procedure. The coefficients of variation for recoveries of metals were 9.2%, 8.2%, 5.1%, 5.6%, 6.5%, 2.8%, 4.3% and 4.8% for Cd, Co, Cu, Ni, Pb, Zn, Cr and Fe, respectively. Three replicate samples were analyzed to determine the analytical and sample precision. Estimated precision was: Ba, 10%; Cd, 10%; Co, 11%; Cu, 7%; Ni, 8%; Pb, 9%; V, 10%; Zn, 9%; Ag, 11%; Cr, 11%; Fe 5%.
RESULTS AND DISCUSSION
The concentrations of metals in fish samples from the study area are presented in Table 1. Most of the metals were found in sub ppm levels. Zinc was the most abundant with concentrations in ppm levels (Table 1). The relative high concentrations of Zn in fish is not dangerous for human health because Zn is an essential element for most living organisms and only becomes toxic at very high concentrations (Heckman 1990). In general, this study found relatively little variation in the concentrations of metals by station and month. This suggests metal concentrations in fish of the Laguna were not influenced by activities of oil and gas dredging in November 1996.
The mean concentrations of metals in fish of the study area were compared with fish from the Gulf of Mexico in Table 2. The concentrations of metals, except Cd and Pb, in fish of the Laguna de Pom-Atasta were equal to or less than the metal contents in the Galveston Bay and the Gulf of Mexico. The results suggest the enhanced bioaccumulation of Cd and Pb in the study area in comparison with fish from non-discharging platforms of the Gulf of Mexico. In a previous study, the relatively higher concentrations of Cd and Pb were found in water samples from the Laguna de Mexico (Vazquez et al. 1998). Anthropogenic sources such as automobile atmospheric deposition, river and industrial inputs were probable causes of higher levels of Cd and Pb.
The concentrations of Cd and Pb were compared to the established metal concentrations in fish by the Secretaria de Salubridad (1993). Secretaria de Salubridad is a health office in Mexico which regulates contamination in the organisms. Both Cd and Pb in fish of the Laguna de Pom-Atasta were lower than the Secretaria de Salubridad established values. Therefore, Cd and Pb levels in fish of the study area are not considered to be dangerous for human consumption.
Table 1. Metal concentrations (mg/kg dry weight) in fish muscle of Pom-Atasta lagoon, Campeche, Mexico. Station Ba Cd Co Cu Ni Pb V Zn Ag Date 1 Oct. 96 0.018 0.44 0.037 0.97 3.16 0.34 0.011 18.5 <0.01 Nov. 96 0.023 0.14 0.043 0.74 1.38 0.20 0.009 23.2 0.19 Jan. 97 0.019 0.14 0.017 0.72 0.58 0.43 0.014 13.2 <0.01 2 Oct. 96 0.027 0.20 0.021 0.64 2.84 0.24 0.012 15.3 <0.01 Nov. 96 0.031 0.40 0.029 0.35 3.26 <0.05 0.010 11.3 0.24 3 Oct. 96 0.018 0.35 0.034 2.17 3.65 <0.05 0.021 27.2 0.15 Nov. 96 0.021 0.14 0.036 0.68 4.30 0.53 0.017 14.5 0.14 Jan. 97 0.023 0.26 0.035 0.55 2.34 0.55 0.016 16.8 <0.01 4 Oct. 96 0.042 <0.01 0.028 0.77 0.96 <0.05 0.012 16.0 <0.01 Nov. 96 0.039 0.23 0.032 0.42 1.87 0.42 0.014 19.1 <0.01 Jan. 97 0.037 0.19 0.036 0.53 0.39 <0.05 0.016 15.1 0.23 5 Oct. 96 0.033 0.29 0.030 0.48 0.24 0.14 0.022 18.3 <0.01 Nov. 96 0.029 0.10 0.027 1.32 <0.01 0.24 0.017 18.3 0.19 Mean 0.028 0.22 0.031 0.76 1.78 0.26 0.015 17.5 0.08 SD 0.008 0.12 0.007 0.48 1.47 0.21 0.004 4.00 0.10 Station Cr Fe Date 1 Oct. 96 0.49 1.65 Nov. 96 0.20 0.59 Jan. 97 1.35 1.10 2 Oct. 96 <0.01 2.15 Nov. 96 0.25 1.50 3 Oct. 96 <0.01 1.68 Nov. 96 <0.01 1.64 Jan. 97 <0.01 1.24 4 Oct. 96 0.77 1.54 Nov. 96 <0.01 0.42 Jan. 97 1.55 0.53 5 Oct. 96 <0.01 0.48 Nov. 96 2.60 1.84 Mean 0.56 1.26 SD 0.78 0.56 Table 2. Comparison of mean metal concentrations (mg/kg dry weight) in fish muscle from the Gulf of Mexico area. Area Ba Cd Cu Ni Pb V Zn Fe This Study 0.028 0.22 0.76 1.78 0.26 0.015 17.5 1.26 GBNEP (1) -- 0.01 1.02 0.04 0.07 -- 21.5 -- Gulf of Mexico (2) 0.06 <0.01 1.0 1.5 0.12 0.93 18.6 8 SS (3) -- 0.50 -- -- 1.00 -- -- -- (1) Galveston Bay National Estuary Program (Park & Presley 1997) (2) Non-discharging platforms in the Gulf of Mexico (Trefry et al. 1996) (3) Secretaria de Salubridad (1993)
This project was supported by the National University of Mexico (UNAM) (Project 132).
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Felipe Vazquez G. and Virender K. Sharma
Instituto de Ciencias del Mar y Limnologia, UNAM
Cd. Universitaria D.F., Apartado Postal 70-305, C.P. 04510, Mexico
and Department of Chemistry, Florida Institute of Technology
150 West University Boulevard
Melbourne, Florida 32901
VKS at: email@example.com
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|Author:||Vazquez G., Felipe; Sharma, Virender K.|
|Publication:||The Texas Journal of Science|
|Date:||Aug 1, 2001|
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