# Effective Uptake of Cadmium and Chromium from Wastewater Using Carbon-Based _Capsicum annuum_
## 1 Introduction  
Several toxic ions such as cadmium and chromium present in water adversely affect the environment and ecosystem [1]. High concentrations of chromium, especially hexavalent chromium [Cr(VI)], are carcinogenic and harmful to aquatic organisms [2]. Chromium accumulates in sediments and water bodies, enters the food chain, and leads to respiratory problems and dermatitis [3]. The World Health Organization (WHO) has recommended a maximum level of 0.05 mg/L for total chromium in drinking water [4]. Chromium concentrations in industrial wastewater are typically between 50-200 mg/L [5]. Cadmium (Cd) is prevalent in rivers and soils worldwide and is carcinogenic [6,7]. Continuous exposure to Cd causes adverse and irreversible neurological damage, osteoporosis, metabolic disorders, kidney failure, and cancer [8]. The limit for Cd(II) concentration set by the WHO and the International Agency for Research on Cancer is below 0.003 mg/L [9]. This pollutant originates from industrial effluents, including electroplating, mining waste, and pigment production [10]. Chromium exists in the environment as Cr(III) and Cr(VI) states, with Cr(VI) being the most toxic. Ingestion, contact, and inhalation are the common routes of chromium entry into the human body. The negative effects of chromium on humans are lung cancer, skin allergies, carcinogenicity, and skin allergies [11]. The presence of heavy metals threatens both the environment and human health and affectsthe production of food fit for consumption [12]. Researchers are constantly looking for technologies that can effectively adsorb toxic pollutants from the environment, especially from the aquatic environment. In general, conventional methods have been used to uptake toxic metals and chemicals from the environment [13]. However, these methods have their limitations, such as high costs, possible secondary pollution, and difficulties in some applications [14]. In addition, various analytical methods have been used for quantifying metal ions, namely mass spectrometry, AAS, ICP, and voltammetry methods [15]. Although these techniques are highly sensitive, they are not suitable for on-site detection because they require expensive instruments that are very difficult to obtain [15]. Optical determination and detection of metal ions has become an important field of research as it can be used in several areas, including biomedicine, chemistry, and environmental research [16]. Currently, adsorption is the most efficient method for adsorbing toxic metal ions from water because it offers advantages such as easy handling and selectivity [17; 18]. Agriculturally based materials have been used as adsorbents for the removal of different pollutants. This is due to their accessibility, availability, low cost, recyclability, and reusability. [PERSON] et al. (2021) [19] synthesised sulfur nanoparticles using a precipitation method and cationic surfactants for photocatalytic reduction of Cr(VI). Studies have shown that biodegradation of industrial dyes can be achieved using physicochemical treatment processes [19]. Several studies used plant material converted into activated carbon to adsorb pollutants from wastewater. Carbon from biomass waste or plant materials is recognized as an environmentally friendly adsorbent, with high efficiency and low cost, for use to immobilize pollutants in water [20]. Carbon from agricultural material is a desirable adsorbent due to its high cation exchange, unique physicochemical properties, high specific surface area, and many functional groups [21]. Carbon materials can meet the demand for inexpensive adsorbents for wastewater treatment [22]. Toxic metal ions and carbon can interact with each other in various ways, including through bonding by ion exchange, precipitation with soluble minerals, and complexation of oxygen functions [23]. Researchers have used activated carbon as an effective adsorbent to adsorb dyes, toxic metal ions, and pharmaceutical pollutants.