## 3 Results and Discussion  
### Earthworm Survival and Growth in Amended Soils  
The biological response of the earthworms significantly depended on the applied soil amendment (Figure 1). The observed mass reduction was diversified from 10% to 100% and was directly related to their mortality. No earthworms survived after adding biosolids to the soil (both GB and BB). After 1 week of the experiment, the earthworms died. We suggest that this effect should be attributed not only to the metal toxicity, but also to the change in living conditions after the application of fresh biosolids. In the case of the other soil amendments, the survival rate (SR) was observed at the level of 40%-93%, but significant changes were only induced by GC and BE (Figure 1). Generally, in all the samples, a reduction in earthworm weight was recorded. The overall decrease was noted in the following order: GC (72%) > BE (33%) > ZC (17%) > CP (15%) > CC (13%) > IO (11%) > RW (10%). The great importance of organic amendments for improving soil quality is well known in remediation systems [2; 3; 14]. However, in our study, some of the amendments adversely affected the survival of the earthworms. One of the potential reasons for the observed mortality due to the application of biosolids is related to the fact that these organic amendments contained additional amounts of TE (Table 1) that could have been easily assimilated by the earthworms. Moreover, the application of biosolids to contaminated soils may increase the bioavailability of metals due to the high amount of destabilized (dissolved) organic matter,  
Figure 1: Changes in the weight and survival rate (SR) of earthworms under the influence of soil amend-ments (n = 3). The weight change was expressed in normalization to the number of surviving earthworms * significant differences at \(p<0.05\) in soil between initial and final weight within a given amendment according to the Tukey test; ZC-Zabrze compost, GC-GWDA compost, BB-Belchatów biosolids, GB-Grabów biosolids, CP-Calcium phosphate, IO-Iron oxide, BE-Bentonite, RW-Rock waste, CC-Limestone. which facilitates metal mobility in soil [3; 13; 14; 15]. According to [PERSON] et al. [15], compost or biosolids may additionally remobilize some elements that are present in highly recalcitrant fractions (residual Fe-oxide and Al oxides). The negative effect of biosolids on earthworms was also observed by other authors in uncontaminated soils [21]. Combined with the fact that the composts tested in our study did not result in such a mortality of earthworms despite applying similar amounts of trace elements to the soil, this might suggest other causes of earthworm death in biosolid-treated soils. The level of mortality could have been related to the transformation of exogenous organic matter, which is less stabilized in biosolids than in biosolid-compost. The more intense mineralization of organic matter in the soil with the addition of fresh biosolids can cause strong oxygen deficiency immediately after its mixing with soils, resulting in the death of earthworms. This is only a hypothesis, however; it needs to be tested in detail in separate biotests. The other commonly applied soil amendments, such as phosphates, iron oxides, calcium carbonate, and clay-rich materials did not affect the survival rate, causing only a slight decrease in the total earthworm weight. These amendments did not bring substantial amounts of potentially toxic trace metals or organic substances to the soil; therefore, their effect on the earthworms was apparently less complex than in case of the biosolids. The effect of these amendments on the earthworms' weight was probably related to the alteration in the TE toxicity due to the amendments. The metals were subjected to immobilization processes after the introduction of these materials to soils, comprising ion exchange, adsorption, occlusion, surface precipitation, and co-precipitation processes. As summarized by [PERSON] et al. [12], many studies assessing the toxicology of metals to earthworms are available in the literature.