# Remediation of Metal/Metalloid-Polluted Soils: A Short Review
## 3 Toxicology
### Health Impacts Over Short, Medium, and Long Term
Different studies have reported the dangerous effects of lead on the neurologic system, such as irritability, agitation, headaches, confusion, ataxia, drowsiness, convulsions, and coma, and has an effect on renal functions, the body development, and the lymphatic system [50]. * Mercury (Hg): in the environment, mercury can be present in the form of both organic and inorganic (Hg, Hg2\({}^{+}\), Hg2\({}^{+}\)) compounds. Mercury tends to deposit in many parts of the human body, damaging the brain, thyroid, breast, myocardium, muscles, liver, kidneys, skin, and pancreas. Among them, the nervous system is the most affected [51]. Inorganic mercury can inhibit the activity of enzymes in the body and destroy the normal metabolism of cells. The organic form has a great negative effect on brain function and can enter through the food chain [52]. * Arsenic (As): it is present in the environment in organic and inorganic forms, the most common and toxic forms are arsenate and arsenite. Arsenate can cause damage to the plant since it affects phosphate metabolism, while arsenite binds to sulfhydryl groups of proteins, interfering with their structures and functions [53; 54]. Chronic exposure to this metalloid causes cutaneous lesions, such as melanosis (hyperpigmentation), keratosis, and leukomelanosis (hypopigmentation); lung, bladder, liver, and kidney cancers; ischemic heart diseases, impaired cognitive abilities, motor functions, and hormonal regulations [55]. If the heavy metal and metalloid concentrations in soil are known, some methods to assess the associated risks are available in the scientific literature. For example, the Hakanson method permits to calculate the potential ecological risk index (RI) [56; 57; 58]:  
\[RI=T_{r}\cdot C_{f}=T_{r}\cdot\frac{C}{C_{n}} \tag{1}\]  
where:  
\(T_{r}\) is the toxic response factor of the element, which reflects the toxicity level and sensitivity of organisms to it [59]. This factor is calculated with an empirical formula, considering the effects that the element can cause in microorganisms. For Cr, Ni, Cu, As, Cd, and Pb, \(T_{r}\) is equal to 2, 6, 5, 10, 30, and 5, respectively;  
\(C_{f}\) is the pollution index of the element, the ratio between the measured concentration of an element in the tested area, \(C\), and the background (to say, natural) concentration of an element in the tested area, \(C_{n}\). The \(RI\) value reflects the state of the soil under examination, according to these assessments:  
* \(RI\) < 150: the ecological risk is low;
* \(150\leq RI\leq 300\): the ecological risk is moderate;
* \(300\leq RI\leq 600\): the ecological risk is considerable;
* \(RI\geq 600\): the ecological risk is very high. Another method that defines the hazard quotient (HQ) [58] is expressed as:  
\[HQ=\frac{C}{C_{b}} \tag{2}\]  
where:  
\(C\) is the measured concentration of an element in a study area;  
\(C_{b}\) is the benchmark concentration of the element (the limit value concentration given by current legislation). If the hazard quotient for the test is lower than 1 (\(HQ\) < 1), negative effects and ecological risks are highly unlikely. Vice versa, if \(HQ\) > 1, the soil must be remediated.