## 3 Results and Discussion
### Residual Levels of Organochlorine Pesticides in Soil  
Organochlorine pesticides are accumulated mainly in soil [18; 47; 48], and their absorption is largely determined by the content of soil organic matter [46; 49]. An analysis of OCP residues revealed the highest average levels of DDT (1.14 \(\mu\)g kg\({}^{-1}\)) (Figure 4a) and lower levels of \(\gamma\)-HCH (0.33 \(\mu\)g kg\({}^{-1}\)). Similar proportions of soil contaminants were reported by [PERSON] et al. [6]. In the cited study, DDT was also the most prevalent pollutant (accounting for 83% of all soil contaminants), which was attributed to its higher persistence as well as the fact that this pesticide had been more widely applied \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Year**} & **Without** & **Mineral** & **MBM \({}^{*}\) 1.0 t** & **MBM 2.0 t** & **MBM 3.0 t** & **Av. for** \\  & **Fertilization** & **Fertilization** & **ha\({}^{-1}\)** & **ha\({}^{-1}\)** & **ha\({}^{-1}\)** & **Treatments** \\ \hline
2014 & 11.68 \(\pm\) 0.29 deg & 12.30 \(\pm\) 0.18 bed & 12.85 \(\pm\) 0.41 ab & 12.35 \(\pm\) 0.10 & & \\  & & & & abcd & 12.75 \(\pm\) 0.12 abc & 12.39 \(\pm\) 0.14 A \\
2015 & 11.20 \(\pm\) 0.11 def & 12.53 \(\pm\) 0.35 abc & 13.30 \(\pm\) 0.09 ab & 12.70 \(\pm\) 0.09 ab & 13.48 \(\pm\) 0.19 a & 12.64 \(\pm\) 0.20 A \\
2016 & 11.10 \(\pm\) 0.35 ef & 10.30 \(\pm\) 0.17 f & 10.63 \(\pm\) 0.21 ef & 12.50 \(\pm\) 0.04 abc & 13.03 \(\pm\) 0.18 ab & 11.51 \(\pm\) 0.26 b \\
2017 & 10.95 \(\pm\) 0.32 ef & 10.85 \(\pm\) 0.23 ef & 10.58 \(\pm\) 0.17 ef & 12.63 \(\pm\) 0.14 abc & 12.65 \(\pm\) 0.22 abc & 11.53 \(\pm\) 0.23 b \\ Av. for Year & 11.23 \(\pm\) 0.15 C & 11.49 \(\pm\) 0.27 C & 11.84 \(\pm\) 0.34 b & 12.54 \(\pm\) 0.06 A & 12.98 \(\pm\) 0.11 A & \\ \hline \hline \end{tabular} \({}^{*}\) MBM—meat and bone meal. Values followed by the same letters do not differ significantly in [PERSON]’s (HSD) test (_p_ < 0.05).  
\end{table} 
Table 2: Soil organic carbon (C\({}_{\text{org}}\)) content, g kg\({}^{-1}\) (mean and standard error). Figure 3: Residual levels of organochlorine pesticides in meat and bone meal (MBM). Values followed by the same letters do not differ significantly in [PERSON]’s (HSD) test (_p_ < 0.05). \(\gamma\)-HCH—\(\gamma\)-hexachlorocyclohexane, DDT—1,1,1-Trichoro-bis-2,2 [4-chlorophenylophenyl]-ethane, DDD—dichloroethen, DDE—dichloroethen, DDE—dichloroethen. than lindane in Poland. Soil \(\gamma\)-HCH levels decreased gradually in all treatments. In 2017, they were reduced by 69% relative to those noted in 2014 (Figure 4a). The concentration of DDT continued to increase up to the third year of the study (by 60.1% on average in 2016 relative to 2014). In the present study, DDE concentration in soil was higher than DDD concentration. Similar observations were made by [PERSON] et al. [50]. The authors concluded that DDT is most likely converted to DDE through the aerobic degradation pathway. In the analyzed soil, DDE concentration was highest in the third year (1.037 ug kg\({}^{-1}\)), and DDD concentration was highest in the fourth year of the study (0.061 ug kg\({}^{-1}\)) (Figure 4a). None of the analyzed fertilization treatments significantly influenced soil \(\gamma\)-HCH levels (Figure 4b). An analysis of the interaction between fertilization treatments and years of the study revealed similar relationships (Figure 5a-d). Fertilization treatments had no significant effect on soil DDT levels, either in terms of average values (Figure 4b) or in experimental years (Figure 5). Similarly to DDT levels, the concentrations of DDT metabolites (DDD and DDE) in soil were not significantly affected by fertilization treatments in the experimental years (Figure 4b) or in terms of average values (Figure 5). The exception was the significantly lower DDD content in the no-fertilization treatment in 2017, compared to the other treatments. Soil \(\gamma\)-HCH levels are affected by environmental processes such as plant metabolism, mineralization, photodegradation, and potential translocation to groundwater [50].