## 4 Discussion
### Comparisons of LC\({}_{50}\) Values with Those of Other Species of Molluscs  
It is difficult to compare the LC\({}_{50}\) values of metals in this species with those in other gastropod species due to the varying ability of closely related taxa or species belonging to the same genus that inhabit the same environments to accumulate metals in water with varying hardness. Using adult _Theodoxus niloticus_ snails, [PERSON] [7] reported the 96-h LC\({}_{50}\) values for Zn, Fe, and Pb to be 12.199, 8.6 and 18 mg/L, respectively. These values grew as the duration of exposure decreased. Fe was the most hazardous element to the snail, followed by Zn and Pb. The findings of this investigation on the sensitivity of _P. insularum_ to the toxicity of heavy metals supported the notion that the susceptibility of an animal to heavy metal toxicity differed among species [55; 56; 57; 58]. This is demonstrated by comparing the LC\({}_{50}\) values of _P. insularum_ to those of other species. For example, [PERSON] and [PERSON] [59] reported that the 96-h LC\({}_{50}\) of Cu in _Physa integra_ was 0.039 mg/L, which is lower than the 96-h LC\({}_{50}\) in _P. insularum_ in the present study, which was 0.21 mg/L of Cu. The variation may be due to the various test animal species, techniques, and environmental conditions. [PERSON] and [PERSON] [60] reported that the 96-h LC\({}_{50}\) values of Cd in the freshwater shrimp _Paratyn tasmaniensis_ were 0.06 mg/L. However, in the present investigation, the 96-h LC\({}_{50}\) values of Cd in _P. insularum_ were 2.55 mg/L. In addition, [PERSON] [61] reported that the 96-h LC\({}_{50}\) values of the tropical freshwater snail _Radix plicatulus_ were 2.55 mg/L of Cd, which was comparable to the 72-h LC\({}_{50}\) values of Cd in juvenile _P. insularum_ (2.15 mg/L) in the present study. Consequently, based on the preceding examples, it can be concluded that the susceptibility of different species [62] and several factors such as experiment procedures, the physical and chemical characteristics of the experimental conditions such as temperature,DO, pH and water hardness [63], as well as the physiological, size, and age of the animals used, can influence the LC\({}_{50}\) values in the toxicity study. Multiple researchers have investigated the impact of environmental characteristics such as temperature, pH, and dissolved oxygen on the toxicity of heavy metals and published their findings in the scientific literature. In general, increasing respiration at higher temperatures directly increased toxicity. Moreover, high temperatures indirectly increase toxicity by reducing oxygen levels in water [64]. Temperature increases had a direct effect on the ramshorn snail, _Helsioma campanulatum_, and the pond snail, _Viviparus benghalensis_, according to [PERSON] et al. [65]. [PERSON] [58] also showed that at 20 \({}^{\circ}\)C, the mummichog was more vulnerable to Cd than at 5 \({}^{\circ}\)C. In contrast, it is well established that increased water hardness reduces the acute toxicity of metals [66]. However, as the temperature utilized in the present exposure investigation was constant, this abiotic parameter had no effect on the snails' toxicity and tolerance to heavy metals. Cu is more hazardous than Zn and Hg to the two intertidal snails _Planaxis sulatus_ and _Trochus radiatus_, according to an acute toxicity test performed by [PERSON] et al. [67] using static bioassay procedures. The availability of heavy metals due to different anthropogenic metal inputs could be attributed to their metal toxicities [68]. For all metals, [PERSON] et al. [9] found that (LC\({}_{50}\) increased with decreasing mean exposure concentrations and periods. Cu was discovered to be the most hazardous metal to _M. tuberculosis_, followed by Cd, Zn, Pb and Ni. Other studies demonstrated divergent patterns in the toxicity of certain snails.