Influence of a Ferronickel Smelting Plant Activity on the Coastal Zone through Investigation of Metal Bioaccumulation on Two Gastropod Species (Patella caerulea and Phorcus turbinatus)

Abstract

JEAT an open access journal In order to investigate the effect of the smelting plant, the distribution of heavy metals along the coastline is presented as seasonal line plots (Figure 2). It can be clearly seen that these plots have a similar pattern in Ph. turbinatus for Fe and Mn; both metals related to the smelting plant activity. The same was observed for P. caerulea with the exception of the very high values in LA2 during winter 2010. The geographical distribution of metals apparently indicates that during the whole duration of the study the sampling stations located closer to the factory (station LA4 and during some seasons station LA5 too) are the most contaminated by Fe and Mn. Zn also showed high concentrations in both species collected at the vicinity of the industry (station LA4). On the other hand Cu presented quite completely different pattern: the higher concentrations were detected in both species in stations LA6 and LA7. In addition Ph. turbinatus collected at station LA3 was heavily impacted by Cu presenting concentrations even higher than those at stations LA6 and LA7. Kruskal Wallis test revealed that all the observed differences were statistically significant (p<0.05). Concerning the seasonality, it has been observed that the two studied gastropods reached their maximum values during different seasons: P. caerulea followed the seasonal pattern of seawater presenting the highest levels during autumn and winter (2009-2010). On the contrary the highest metal concentrations in Ph. turbinatus were measured in spring. For both species the seasonal differences were statistically significant according to the Kruskal Wallis test (p<0.05). Note that data from the reference stations, because of their limited number, due to technical reasons excluded from the statistical tests. In order to find out if the elevated metal concentrations in seawater and especially the dissolved ones related to the metallurgy industry which resulted in higher bioaccumulated levels in gastropods, correlation analysis was performed (Table 2). Additionally, correlation analysis was also applied to bioaccumulated metals in order to find out if any relation exists among them. The two species of gastropods seem to present different sensitivity to seawater quality; for Ph. turbinatus a significant positive correlation (p<0.01) was found between concentrations of the dissolved Fe and Mn in seawater and the accumulated amount in its soft tissues, as for P. caerulea a significant positive correlation (p<0.01) was found between concentrations of the dissolved Zn in seawater and the accumulated amount in the soft tissues (Table 2). Concerning the interrelation of the bioaccumulated metals the positive significant correlation can be mentioned for both species between Fe and Mn with Zn and Mn with Fe (Table 2). It is also interesting to cite the order of magnitude of the bioaccumulated metals: in P. caerulea metal concentrations decrease in the following order: Fe>Zn>Cu>Mn while in Ph. turbinatus the metals are following a quite different order of magnitude: Fe>Cu>Zn>Mn. The Bioconcentration Factor (BCF) may be used to evaluate the bioaccumulation ability of a species in an ecosystem [18]. The formula used for the calculation is BCF=Co/Csw, where Co is the mean concentration of metals in the organism in µg/g dw and Csw is the equivalent concentration in seawater in µg/l [20]. The calculated Bioconcentration Factor (BCF) for the two studied gastropods indicates that Ph. turbinatus presented higher bioaccumulation capacity for Mn and Cu while P. caerulea got better ability in accumulating Fe (Table 3). Finally in order to establish a better relationship between the different parameters in this study, a cluster analysis was run. This is a unique method which groups the cases that share the same variables. Ward's method and Euclidean distance were applied for this analysis. Both seawater and gastropod samples were stored in polyethylene bottles and polyethylene bags and brought to the lab in isotherm boxes. Heavy metals in dissolved phase were pre-concentrated on Chelex-100 resin columns [22]. The soft tissues of gastropods were separated from the shells and during each sampling occasion 8 to 12 pooled samples were prepared for each species containing 10 individual tissues of P. Caerulea (range size of 22-35 mm) and 15 of Ph. turbinatus (range size of 25-37 mm) respectively. Samples were freeze dried and homogenized. About one gram of dried tissue was digested with 6 ml of concentrated HNO 3 (65%) (Merck) and 2 ml of concentrated H 2 O 2 (30%) (Merck) in microwave digestion system (CEM-MDS 2100) and consequently diluted up to 20 ml with Milli-Q water. Blanks were carried out in the same way. Two groups of heavy metals were measured by Flame atomic absorption: Fe and Mn related to the smelting plant activity and Cu and Zn related to urban activities. The accuracy of the analytical procedure was checked by certified references materials. For water samples the certified reference material CASS-4 and spiked seawater and for biota samples CRM NO 279 (Ulva) and NIST 2976 (Mussel tissue) were used. The test revealed more than 90% recoveries for all metals including the water and biota samples. The statistical treatment of the data comprised control for normality and homogeneity with Levene's test, check for statistically significant differences among median concentrations of the various data sets with the Kruskal Wallis test and finally Cluster analysis (CA) in order to illustrate the similarities among sampling stations. Results In total 28 samples of seawater, 181 samples of Ph. turbinatus corresponding to 2715 individuals and 254 samples of P. caerulea corresponding to 2550 individuals were measured for Fe, Mn, Zn and Cu. Summary statistics including average concentrations and range of metals in biota and seawater are presented in Table 1, expressed in μg/g dry weight and µg/l respectively. It is easily observed that the two gastropod species bioaccumulated metals in different degree: P. caerulea had higher Zn and Fe concentrations, whilst Ph. turbinatus had higher Mn and Cu levels. The observed differences are notable; indeed Mn and Cu in Ph. turbinatus are respectively two and five times higher than those in P. caerulea and the concentrations of Zn and Fe in P. caerulea are twice higher than that in Ph. turbinatus. As expected, metal levels in water were significantly lower than those in the gastropods. Figure 1: Map indicating the location of the sampling stations in N. Evoikos Gulf.