## 3 Results and Discussion
### Seasonal and Spatial Variation of Heavy Metal Content
These metals are also used in the industries of DEPZ pigment and reducing agents; cotton processing, soldering and welding flux; rubber industry, glass, enamels, plastics, lubricants, cosmetics, pharmaceuticals, agents for burns and ointments [40]. Both metals were unevenly distributed in the study area (Figure 4). Both metals showed higher concentration in a similar study area to [PERSON] and Gani [37]. Figure 3: Seasonal and spatial variation of (**a**) Mn and (**b**) Cu in the study area. Pb contamination in soils has been seriously emphasized in recent years since this metal is very toxic for humans and animals [32]. Pb enters human or animal metabolism via the food chain. Pb production and operation facilities without a waste-gas treatment system, battery production and scrap battery recovery facilities, thermal power plants, and iron-steel industries are the other lead sources. Moreover among the heavy metals, Pb is the most immobile element and its content in soil is closely associated with clay minerals, Mn-oxides, Al and Fe hydroxides, and organic material [32]. Although there was point wise variation in concentration of Pb (Figure 5), a very limited average variation was observed over two seasons. Pb concentrations in Gebze soils were between 17.07 and 8,469 mg/kg with an average of 246 mg/kg which is noticeably higher than values reported in the literature [32]. The average Pb concentration in the soils of the Thrace region was recorded as 33 mg/kg [41]. Long term exposure of Pb is risky. Bioaccumulation and bio-magnification can take place. Hence, regular consumption of vegetables from this area by residents could pose a serious neurological health problem from long term Pb exposure. Figure 4: Seasonal and spatial variation of (**a**) Zn and (**b**) Cr in the study area. Figure 5: Seasonal and spatial variation of (**a**) Pb and (**b**) Hg in the study area. Hg is a toxic metal for environmental and human health. Base-metal processing and some chemical industrial activities are the main source for Hg contamination in soils. Mining activities, sewage wastes, and the use of fungicides also result in Hg pollution. The dry season contained about four times higher concentrations of this metal than that of the wet season (Figure 5). Seasonal rainfall may limit the concentration in soil during the wet season. Hg concentration in Gebze soils was between 9 \(\upmu\)g/kg and 2,721 \(\upmu\)g/kg with an average of 102 \(\upmu\)g/kg [32], which is very much lower than present work. Average concentration of Ni in the dry season was higher than the wet season (Figure 6). Major sources of Ni in the soil are poorly treated wastewater that is discharged from ceramics, steel and alloys and other metal processing industries. Long term exposure of Ni through the food chain may contribute to health problems like skin allergies, dermatitis, rhinitis, nasal sinusitis, lung injury and nasal mucosal injury [38]. There is a growing environmental concern about Cd being one of the most eco-toxic metals, exhibiting highly adverse effects on soil health, biological activity, plant metabolism, and the health of humans and animals [33]. The comparison of mean concentrations of heavy metals in the soil of the study area with the official Indian standard [35], and the MAC of elements in agricultural soil in China [34] showed that only the concentration of Cd was found to be 3-fold higher than the threshold level of India and 19 times higher than the Chinese standard (Figure 6). Higher concentration of Cd in the wet season may be due to more Cd containing waste water release from DEPZ compared to that of the dry season. The Cd concentrations in Gebze, Turkey soils varied from 0.05 to 176 mg/kg and the average was 4.41 mg/kg [32]. The average Cd concentration in northern Poland soils was 0.80 mg/kg [36] which is significantly lower than that in Gebze soils. Environmental levels are greatly enhanced by industrial operations as Cd is commonly used as a pigment in paint, plastics, ceramics and glass manufacture.