Assessment of mercury contamination of the Svitava and Svratka rivers and muscle of chub (Leuciscus cephalus L.) in the urban agglomeration of Brno in the Czech Republic

This study focused on the total mercury and methylmercury content in the muscle of chub (Leuciscus cephalus L.), the total mercury in the river sediments and the evaluation of health risks associated with fish contamination. Chub were caught at seven localities on the Svratka and Svitava rivers in the agglomeration of Brno in 2008. The results were compared to those obtained from the same sites in 2007. Total mercury was determined by atomic absorption spectrophotometry using an AMA 245 analyzer, and methylmercury was determined by gas chromatography (using an electron-capture detector) after acid digestion and toluene extraction in chub muscle. The highest concentrations of total mercury and methylmercury (0.12 ± 0.14 and 0.07 ± 0.02 mg·kg-1 fresh weight, respectively) were found in Svratka before junction (south of Brno), whereas the lowest concentration of mercury and methylmercury in chub (0.06 ± 0.01 and 0.04 ± 0.01 mg·kg-1) was detected in Svitava before junction with the Svratka River. Total mercury in sediments ranged from 0.01 to 1.05 mg·kg-1 dry weight, the highest value was detected in the sediment from Rajhradice. The lowest content (0.01 mg·kg-1) was at Kníničky. Hazard indices calculated for the selected localities showed no health risk for either a standard consumer or a fishing family. Fish from the Svitava and Svratka rivers show very low mercury concentration and hazard index and their consumption poses no health risk from total mercury and methylmercury contamination. Czech river, Leuciscus cephalus, methylmercury, sediment, total mercury Mercury pollution is a ubiquitous problem with atmospheric deposition contaminating watersheds in areas far from anthropogenic or natural atmospheric point sources (Swain et al. 1992). Several forms of mercury are present in the aquatic environment, including elemental, ionic, and organic (Morel et al. 1998). In most freshwater, ionic mercury in the divalent state (HgII) is the predominant form, whereas in most fish species more than 95% of mercury occurs as methylmercury (MeHg). Thus, the conversion of ionic mercury to MeHg is an important link in the bioaccumulation of mercury in fish and ultimately in its toxicity to humans and wildlife (Eisler 2006). Methylmercury is the most toxic form and bioaccumulates in fish primarily through dietary uptake (WHO 1990). The level of bioaccumulation is a function of age, species, and tropic transfer. Methylmercury exposure can affect growth, reproduction, development and survival in fish (Weiner and Spry 1996). Halbach (1995) reported that bioaccumulation of mercury in fish and its toxicity in humans can be attributed to the high affinity of mercury for sulphur-containing proteins such as metallothioneins and glutathione. The highest concentration of mercury in fish is contained in muscle, and thus muscle is a good indicator of mercury contamination (Čelechovská et al. 2007). A project of the Ministry of Education Youth and Sport of the Czech Republic comprised a two year study (2007 and 2008) focusing on mercury contamination of the Svitava and Svratka rivers (Czech Republic). In addition to mercury contamination, the project included assessment of persistent organic pollutants using selected ACTA VET. BRNO 2011, 80: 227–233; doi:10.2754/avb201180020227 Address for correspondence: Ing. Kamila Novotná Kružíková, Ph.D. Department of Veterinary Public Health and Toxicology University of Veterinary and Pharmaceutical Sciences Brno Palackého 1–3, Brno, Czech Republic Phone: +420 541 562 783 Fax: +420 541 562 790 E-mail: [email protected] http://www.vfu.cz/acta-vet/actavet.htm biochemical markers in chub (Blahová et al. 2009, 2010), and passive sampling for monitoring endocrine disruptors (Grabic et al. 2010). The present report summarizes mercury contamination in chub in 2008, and compares the results with those from 2007 (Kružíková et al. 2009). The main aims of the present study were to determine total mercury (THg) and MeHg (methylmercury) concentrations in chub muscle from 7 localities on the Svitava and the Svratka rivers in the Brno agglomeration, to assess THg concentration in sediment at these localities, to evaluate health risks associated with consumption of fish from these sites and to compare data from 2007 and 2008. Materials and Methods Sampling sites Mercury contamination was assessed in the Rivers Svitava and Svratka which run through Brno, the second largest city in the Czech Republic (population 366,680). Brno is an important industrial city with highly developed engineering, chemical, textile, and food-processing industries. Domestic waste, sewage, and other effluents from industrial sources are the most likely source of persistent pollutants in the area’s aquatic ecosystem. The Svratka River runs 29 km through the city and is the major source of water for the Kníničky reservoir, a popular recreation area in the northwest part of Brno. The Svitava River flows through the city for about 13 km and merges into the Svratka River downstream of Brno and is the main tributary to the Svratka River. Seven sites were chosen to evaluate the influence of Brno on mercury contamination of fish and sediments. Two sites were on the Svitava River: (1) Bílovice nad Svitavou, 18 river km; and (2) Svitava before junction, 0.6 river km. Five sites were on the Svratka River: (3) Kníničky, 56.2 river km; (4) Svratka before junction, 40.9 river km; (5) Modřice, 38.7 river km; (6) Rajhradice, 35.0 river km; and (7) Židlochovice, 30.0 river km. Sites 1 and 3 situated upstream of Brno characterize conditions upper of the city. Sites 2 and 4 are situated downstream of Brno and above the confluence of the two rivers. Site 5 is located downstream of a sewage treatment plant and characterizes the Svratka River in areas of waste water effluent. Sites 6 and 7 situated below Brno represent the cumulative effects of all other sites. Weirs are situated between sites 1 and 2, 3 and 4, 5 and 6 and 6 and 7. Fig. 1 shows the locations of the sites. 228 Fig. 1. Map of the study area in Czech Republic: location on Svitava River (Bílovice nad Svitavou, Svitava before junction) and Svratka River (Kníničky, Svratka before junction, Modřice, Rajhradice, Židlochovice). Sampling of fish and sediments In 2008, 119 chub (Leuciscus cephalus L.) were captured by electrofishing, immediately weighed, measured for total length, and scales collected for age determination. Sex was determined macroscopically. For THg and MeHg analysis, muscle samples were taken from the cranial area dorsal to the lateral line, placed in polyethylene bags, labelled, and stored at -18 °C. Table 1 shows the main biometric characteristics of fish collected in 2008. Sediment was sampled from the same locations in February, March, and September. At each location (both years), composite bottom sediment was collected into dark glass bottles, lyophilized in the laboratory, and stored at -18 °C. Sampling was validated in accordance with ISO 5667 12 norm. Determination of THg and MeHg The THg content in muscle and in sediments was determined by cold vapour atomic absorption spectrometry using AMA 254 analyzer (Altec Ltd., Czech Republic).. The MeHg content was determined in the form of methylmercury chloride by gas chromatography (Caricchia et al. 1997). Samples were prepared by acid digestion and extraction with toluene (Maršálek and Svobodová 2006). A Shimadzu capillary gas chromatograph with an electron captured detector GC 2010A (Shimadzu Kyoto, Japan) was used for analysis. A capillary column DB 608 (30 m × 0.53 mm × 0.83 μm; J&W Scientific Chromservis, Czech Republic) was used. Data evaluation was made with GC Solution software (Shimadzu Kyoto, Japan). Limits of detection for THg and MeHg were 1 μg·kg-1 and 21 μg·kg-1, respectively. The limit of detection was set as a sum triple the standard deviation of a blank and a blank mean value. The accuracy for THg and MeHg values was validated using standard reference material BCR-CRM 464 (Tuna Fish, IRMM, Belgium). The total mercury and MeHg concentrations in fish muscle are given in mg kg-1 fresh weight (FW), and THg in sediment is given as dry weight (DW). Health hazard assessment The hazard index was calculated according to Kannan et al. (1998) using a reference dose for THg (0.3 μg·kg-1body weight day-1) set by the United Stated Environmental protection Agency (US EPA). To determine the maximum safe consumption of fish, a provisional tolerable weekly intake limit (PTWI) of 1.6 μg MeHg kg-1 body weight week-1 was used (WHO 1990). The amount of fish safe to be eaten per week was calculated. Statistical analysis The statistical analysis of the data was performed using STATISTICA 8.0 for Windows (StatSoft CR). The data were analyzed with the parametric ANOVA Tukey’s HSD test.