Chemometrics methods for the investigation of methylmercury and total mercury contamination in mollusks samples collected from coastal sites along the Chinese Bohai Sea
Introduction
Mercury is an important but toxic element. Both the direct drainage of industry wastewater and rainwater run-off leads to mercury contamination in oceans. The toxicity of mercury is well known since the notorious poisoning accident at Minamata Bay in southern Japan during 1950s and 1960s (Kurland et al., 1960). This tragic event was due to the consumption of methylmercury-contaminated fish and 48 persons died. Mercury is first absorbed by phytoplankton and then by various consumers within the oceanic ecosystem. Its virulence effect cannot be eradicated for many years. Although the discharging of mercury compounds directly to waterways has been increasingly regulated or prohibited since that time (Douglas, 1994), the deposited mercury still exists in sediments and releases to waters and mercury continues to be released to the atmosphere (Mason et al., 1994). Elevated levels have been found in water and fish samples even in areas far from major sources (Sorenson et al., 1990, Slemr and Langer, 1992, Nater and Gringal, 1992).
Mercury presents in several forms previous works have determined (Westöö, 1966, Hintelmann and Wilken, 1993, Ramalhosa et al., 2001, Liang et al., 2003). Because MeHg is the most toxic forms, the determination includes not only HgT content but also MeHg content.
Mollusks, which lie in the second trophic level in this ecosystem, are popular seafood and long-term consumption of them may result in MeHg accumulation in human body. In previous works, directions for monitoring marine pollution (Goldberg and Bertine, 2000) and implications in estimation of metal bioavailability in Mussel Watch programmes have been recommended (Soto et al., 2000, Szefer, 2000, Szefer, 2002). Organisms Mytilus spp. have been considered to be potential biomonitors of toxic metals in marine ecosystems (Fowler and Oregioni, 1976, Koide et al., 1982, Szefer et al., 1997, Szefer et al., 1999, Szefer et al., 2000, Chase et al., 2001).
Trace metal concentrations in mollusks are not just related to the metal concentrations in the environment. They are also affected by other factors, including mollusk size, growth rate, age, sex, allometric growth ratios, reproductive condition, position in the intertidal zone, sea water salinity, temperature and trace metal interaction with other pollutants in the environment. Even when all known sources of variation in the mollusks are taken into account, and a careful sampling is performed to avoid these sources of variation, variability is still encountered (Borchardt et al., 1988, Lobel et al., 1991).
So, in this study, nine kinds of mollusks were selected to investigate the pollution levels of MeHg and HgT in eight sampling sites and to try to find the biomonitors of mercury in the area of the coastal sites along the Chinese Bohai Sea. The sampling was carried out twice in July to August 2002 and 2003. In addition, in order to compare the relationship between MeHg and HgT, mollusks samples were collected from Hongqiao market, which locates in Beijing city, from the January to March 2003.
Section snippets
Sampling
Fig. 1 shows eight sampling sites. These sites spread out around the Bohai Sea. The collected mollusks were depurated in filtered seawater for approximately 24 h before transported to the laboratory with ice freezing. Stainless steel scalpel blades were used to cut open the mollusks and remove the soft tissues, which were then thoroughly rinsed with Milli-Q water to remove extraneous material and homogenized by blender and stored in glass bottles at −18 °C until analysis. Different species of
Concentration of HgT and MeHg
In order to prove the validity of the method, we analyzed certified reference materials and the recoveries are reported in Table 2. The found values of HgT and MeHg were in good agreement with the certified values, suggesting the proposed method was feasible in the determination of Hg in biota samples. The limit of detection (LOD) HgT and MeHg was 0.70 and 0.15 ng g−1, respectively.
Based on the investigation of Zhang (2001), the main Hg pollution area of Bohai Sea was the northland. In 2001,
Conclusion
The contamination levels of MeHg and HgT in nine species of mollusks sampled from eight coastal sites along the Bohai Sea were investigated. Comparing with twice samples (at an interval of one year), we found that the results were rather different. On the whole, the concentration of MeHg and HgT of the second is lower than the first. Because of the lack of reference points for comparison, the reasons of these were not known yet. The further work is going on. Chemometrics methods were performed
Acknowledgements
This work was jointly supported by National Natural Science Foundation of China (20137010, 20205008) and Chinese Academy of Sciences (KZCX2-414). We acknowledge Professor F.C. Adams for his kindly offering CRM DORM-2.
References (43)
- et al.
Methylmercury in mollusks along the French coast
Marine Pollution Bulletin
(2001) - et al.
An assessment of selenium to mercury in Greenland marine animals
The Science of the Total Environment
(2000) - et al.
Toxicological aspects associated with the ecology of Donax trunculus (Bivalvia, Mollusca) in a polluted environment
The Science of the Total Environment
(1999) - et al.
Trace metals in mussels from the N.W. Mediterranean
Marine Pollution Bulletin
(1976) - et al.
Beyond the Mussel Watch-new directions for monitoring marine pollution
The Science of the Total Environment
(2000) - et al.
The identification of novel biomarkers of renal toxicity using automatic data reduction techniques and PCA of proton NMR spectra of urine
Chemometrics and Intelligent Laboratory Systems
(1998) Methylmercury in rainbow trout (Oncorhynchus mykiss) from Lakes Okareka, Okaro, Rotomahana, Rotorua and Tarawera, North Island, New Zealand
The Science of the Total Environment
(1995)- et al.
Metals and transuranic records in mussels shells, byssal threads and tissues
Estuarine, Coastal and Shelf Science
(1982) - et al.
Simple solvent extraction technique for elimination of matrix interferences in the determination of methylmercury in environmental and biological samples by ethylation-gas chromatography-cold vapor atomic fluorescence spectrometry
Talanta
(1996) - et al.
Speciation analysis of mercury in seafood by using high-performance liquid chromatography on-line coupled with cold-vapor atomic fluorescence spectrometry via a post column microwave digestion
Analytical Chimica Acta
(2003)