# Adsorption of Emerging Pollutant by Pecan Shell-Based Biosorbent
## 1 Introduction  
Recently, the production and consumption of different classes of antibiotics in human and veterinary medicine has been increasing greatly [1]. Due to the low percentage of metabolism in the body (10-50%) a significant portion of antibiotics and their metabolites is excreted through urine and feces in their unaltered form. Antibiotics access the environmental matrices without any restrictions because of the inefficiency of wastewater treatment plants (WWTPs) in completely eliminating this class of contaminants, which are called emerging pollutants [2, 3]. Although the access of antibiotics to aquatic matrices occurs at trace levels (ug L\({}^{-1}\) and ng L\({}^{-1}\)), the continuous introduction of this type of contaminant in the environment poses potential risks to both humans and the environment due to its cumulative effect [4]. The presence of this class of microcontaminants may result in several endocrine disturbances to the local flora and fauna, increased toxicity in the environment, and the presence of antibiotics in aqueous matrices; these leads to the emergence and perpetuation of multidrug-resistant pathogen genes [5].  
Fluoroquinolones (FQs) are a class of synthetic antibiotics widely used in human, veterinary, and aquaculture medicine due to their broad spectrum of antimicrobial action and the inhibition of the DNA gyrase of bacteria as a mechanism of action; this results in a fast antibacterial action. Among the most used FQs, ciprofloxacin (CPX) stands out. Its average annual prescription is 33,000 kg, resulting in a wide distribution of this contaminant in environmental matrices [6]. CPX has already been identified in surface waters at concentrations of 1.56-7.14 ng L\({}^{-1}\), in hospital wastewater at concentrations of 8.95 ng L\({}^{-1}\)[7] and in WWTPs at concentrations of 185-613 ng L\({}^{-1}\)[8]. Numerous toxic andmutagenic effects of the presence of this pollutant have been reported, such as oxidative stress and cellular damage; this may lead to neurotoxic damage in _Daphnia magna_[9], in addition to being associated with the possibility of inhibiting the photosynthesis of some plants, thus resulting in morphological abnormalities [2; 6].  
Due to this reality, many efforts have been made in an attempt to develop viable and effective methodologies for the removal of this class of contaminants from water resources, or for its degradation. Currently, adsorption is one of the most applied procedures because of its wide versatility of application, high efficiency, low toxicity, and ease of processing and operating [10; 11]. Developing Latin American countries are major producers of agricultural products. Brazil, for example, with its vast agricultural production, generates around 298 million tons of bio-waste, originating from sugarcane, rice, soybean, and wheat crops. These bio residues are often underestimated, which ignores the fact that this huge amount of agro-industrial waste can serve another purpose in the industry [12].  
Thus, the present work aims to develop and characterize a biosorbent produced from agro-industrial waste of pecan (_Carya illinoinensis_), extremely common in Brazil, in this case its shells, to explore the adsorption capacity against the antibiotic CPX in an aqueous matrix, analyze its parameters (pH, temperature, contact time, and CPX concentration), and investigate adsorption mechanisms.