Phytotoxicity by Lead as Heavy Metal Focus on Oxidative Stress

In the recent years, search for better quality of life in urban areas has been provoking an increase in urban agriculture. However, this new way of agriculture can bring risks to human health since this land is highly contaminated, due to anthropogenic activities. This way, lead (Pb) phytotoxicity approach must be taken into consideration since it can be prejudicial to human health through food chain. Pb is a common environmental contaminant, which originate numerous disturbances in plant physiological processes due to the bioacummulation of this metal pollutant in plant tissues. This review, focus on the uptake and interaction of lead by plants and how it can be introduced in food chain. Special attention was taken to address the oxidative stress by lead regarding the effects produced in plant physiological and biochemical processes. Furthermore, the antioxidant defence system was taken into consideration. Phytoremediation is applied on site or chronic polluted soils. This emerging technique is useful to bioaccumulate, degrade or decrease risks associated with contaminants in soils, water or air through the use of hyperaccumulaters. In addition, the impact of nanoparticles in plant science was also focused in this article since some improving properties in plants have been increasingly investigated. 1. General Introduction Metals occur naturally in the environment as constituents of the Earth’s crust [1]. They tend to accumulate and persist in the ecosystems due to their stability and mainly because they cannot be degraded or destroyed. Plants absorb numerous elements from soil. Some of the absorbed elements are referred to as essentials because they are required for plants to complete their life cycle. Certain essential transition elements such as iron, manganese, molybdenum, copper, zinc, and nickel are known as micronutrients because they are required by plants in minute quantity [2]. Other transition metals such as silver, gold and cobalt [3, 4], and nontransition elements like aluminum [5] have proven to have a stimulatory effect on plant growth, but are not considered essential. Moreover, it has been documented elsewhere that plants also absorb elements which have no known biological function and are even known to be toxic at low concentrations. Among these are the heavy metals arsenic, cadmium, chromium, mercury, and Pb. However, even micronutrients become toxic for plants when absorbed above certain threshold values [6]. 2. Lead (Pb) Lead (Pb) is a silvery-white highly malleable metal. Among his physical properties, at normal environmental