# Mercury Contents in the Liver, Kidneys and Hair of Domestic Cats from the Warsaw Metropolitan Area
## 4 Discussion  
The obtained results indicate that all of the examined individuals were subject to low, long-term exposure to mercury, which was corroborated by the moderate levels detected in all investigated tissues of older cats. Exposure can be determined based on mercury contents in hair of 0.025 mg\(\cdot\)kg\({}^{-1}\), because hair is a biological material which is not affected by temporary fluctuations of mercury levels in the organism. The liver and kidneys are typically used as indicator tissues, in which essential and toxic trace minerals are deposited. However, their observed concentrations do not always reflect the load of the given element \begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline
**Analyzed** & **Living** & **N** & **Arithmetic** & **Median** & **Min** & **Max** & **Q1** & **Q3** & **SD** \\ \cline{3-10} **Material** & **Conditions** & & & & & & & & & \\ \hline Liver & & & 0.038A & 0.030 & 0.001 & 0.200 & 0.010 & 0.050 & 0.036 \\ \hline Kidney & U & 47 & 0.032B & 0.030 & 0.000 & 0.150 & 0.010 & 0.040 & 0.029 \\ \hline Hair & & & 0.031C & 0.020 & 0.000 & 0.100 & 0.010 & 0.050 & 0.024 \\ \hline Liver & & & 0.020D & 0.010 & 0.000 & 0.090 & 0.010 & 0.030 & 0.020 \\ \hline Kidney & S & 38 & 0.017E & 0.010 & 0.000 & 0.080 & 0.010 & 0.020 & 0.017 \\ \hline Hair & & & 0.017F & 0.010 & 0.000 & 0.080 & 0.010 & 0.020 & 0.016 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Mercury contents depending on living conditions in milligrams per kilogram. Figure 1: Mercury contents depending on age group: 1—cats (1–5 years); 2—cats (6–10 years); 3—cats (11–15 years). on the entire organism [32]. Hair, while being a stable and easy-to-store material, also has the capability to concentrate metals to a lesser degree than other tissues [42; 46]. Indeed, the capability to accumulate metals is affected by the morphology of hair, which varies between species; however, it has been experimentally demonstrated that mercury has a high capability to bind with hair structures, which is why it has become one of the most important analytical materials used in the determination of contents of this metal [47; 48]. Sensitivity to the toxic effect of mercury is a species trait. In light of previous research, it was determined that, among terrestrial mammals, large animal species are more resistant to the toxic effect of mercury [49; 50]. The mechanisms of this phenomenon are not fully understood, yet it appears to be linked to the rate of metabolic change, the capability for organism detoxification, as well as the position of the given species in the trophic chain, because the capability of mercury migration and biomagnification in the food chain of mammals has been thoroughly documented [49; 50; 51; 52]. Predators found at the top of the food pyramid are naturally more exposed to mercury bioaccumulation [4]. Thus far, no reference values for mercury contents in individual tissues of the domestic cat have been determined. Its concentrations registered in mammals subject to fatal poisoning, expressed in mg\(\cdot\)kg\({}^{-1}\) of organ wet weight, are as follows: 6.0 in the brain, 10.0-55.6 in the liver and 37.7 in the kidneys [52; 53]. It has been experimentally demonstrated that LD\({}_{50}\) for the domestic cat is 0.25 mg of mercury per one kilogram of body weight with long-term administration. On day 68, animals started to demonstrate neurological symptoms which continued until the end of the study, i.e., by day 90 of the experiment. In the surviving individuals, the levels of mercury in the liver were 40.2 and 18.1 mg\(\cdot\)kg\({}^{-1}\) of organ wet weight, respectively, for the total mercury content [50]. These are the results of an experimental study aiming at the determination of LD\({}_{50}\) for individuals of the species; thus, the obtained values are extremely high.