# Ecotoxicological Assessment of Soils Reclaimed with Waste
## 4 Discussion  
Analysis of the chemical properties of the soil after remediation showed that the pH increased from 4.7 to 6.1-6.7. Already at this value, Pb sorption increases rapidly, and Zn is transformed into insoluble forms (e.g., Zn(OH)\({}_{2}\), carbonates), reducing its bioavailability. The soil sorption capacity increased to 60-92%, and the organic matter content to 4.8 g/kg, which supports metal complexation and stabilization in the soil [20]. Analysis of GI for root length shows that record-high inhibition (\(\approx\)75%) occurred in the degraded soil without amendments. The sewage sludge treatments showed a significant decrease in GI to approximately 35%, and after adding wool and lime (or NPK), the GI value decreased to 5-10%. These results indicate a synergistic effect of the remediation components. The literature confirms that sewage sludge phytotoxicity decreases with time and organic matter stabilization--[PERSON] et al. (2012) reported a 55-81% GI reduction after a 29-month period. Similarly, in the case of composting, more stable sludges were found to have GIs in the 40-86% range, while less processed sludges achieved lower GIs (2.9-45.8%) [21]. Organic matter stability and limited metal mobility (especially Cu, Zn, and Pb) correlate with higher GI values and lower phytotoxicity. Analysis of the mortality rate (M) reveals the strong phytotoxic effects of sewage sludge, especially when combined with remediation additives. The control variant showed M \(\approx\) 200%, while the combinations of sewage sludge with lime and wool/NPK showed extreme values--from 500% to 1000%. Such high mortality means that, in some cases, the number of dead organisms exceeded the initial population many times over. The literature confirms that even low concentrations of sewage sludge (3-6%) can cause serious phytotoxicity [22]. Moreover, sludge stabilization processes (composing, thermal treatment) significantly reduce its toxicity--composted sludge has a GI of 40-86%, while non-composed sludge has a GI of 2.9-45.8% [21; 23]. Root growth inhibition (GI) is a recognized indicator of environmental phytotoxicity, which reflects the presence of harmful substances that hinder the development of the plant root system [24; 25]. The highest degree of root growth inhibition, reaching 75% in non-reclaimed soil, is confirmed by the extremely unfavorable habitat properties of degraded soil, resulting from, among other factors, the presence of heavy metals, nutrient deficiency, and improper physical structure [26]. The usefulness of municipal sludge as a source of organic matter and microelements was supported by its ability to enhance root development [27]. Regarding mineral wool waste in the study, its presence supported root development by improving water and air conditions and limiting the availability of heavy metals [28]. The synergistic effect of three components--post-flotation lime, municipal sewage sludge, and waste mineral wool--favors the reconstruction of the biological properties of the soil [29]. Unfavorable physicochemical properties and high concentrations of toxic substances are typical for anthropogenically degraded soils [26]. Improving the pH and providing macronutrients alone is not sufficient to effectively neutralize organic pollutants and heavy metals in degraded soils [30]. The beneficial effect of using municipal sewage sludge alone or in combination with other waste is confirmed by previous studies indicating the positive impact of sewage sludge on the biological activity of soils and their remediation potential [31; 32; 33]. Mineral wool can act as a physical barrier limiting the migration of pollutants and as a sorbent for heavy metals [28]. The presence of both sorption material and organic substances (e.g., sewage sludge) promotes the development of microorganisms responsible for the biodegradation of pollutants [27].