World Aquaculture September 2018

WWW.WA S.ORG • WORLD AQUACULTURE • SEP TEMBER 2018 53 (Han et al . 2001, Burridge et al . 2010). Although heavy metals exist naturally in water bodies and bottom sediments (Engin et al . 2015), accumulation of heavy metals in water poses a risk to human and environmental health (Ali et al . 2013). Heavy metals tend to accumulate in sediment and thus heavy metal concentrations are often much higher in sediments than in water (Dummee et al . 2012). Aquatic organisms that live in polluted sediments often bioconcentrate heavy metals in their tissues (Li et al. 2009). Fish can absorb water and compounds from sediments contaminated with heavy metals through the skin and gills (Ranasinghe et al . 2016). In aquaculture environments, Malik et al. (2010) evaluated the bioaccumulation of heavy metals, including Zn, Pb, Cd, Ni, Cu, Cr and Hg in freshwater fish tissues and found that different fish organs accumulated varying quantities of metals. Despite measured accumulation, the concentration of heavy metals was within maximum permissible standard values for human consumption. Laboratory experiments by Feldlite et al . (2008) showed no detectable levels of As, Cd, Hg, and Pb in fish flesh reared in recycled wastewater over two years, but levels of other heavy metals (Cd and Pb) in liver and bones of some fish were above the food standard. In addition to fish, plants raised in aquaponics systems might also become contaminated with heavy metals. Heavy metals can accumulate in plant tissue, posing a potential health risk to consumers when ingested (Rana et al . 2011). As water from system circulates through plants (Miller et al . 1982), water loss occurs from the leaves through transpiration, but heavy metals do not transpire, resulting in accumulation of minute levels of metals in the leaf tissue over time. Contamination with heavy metals levels can damage plant cellular processes (Burzynski and Klobus 2004) and reduce plant size (Santala and Ryser 2009). About 400 plant species are known as metal hyper- accumulators because they can accumulate metals in above-ground tissues (Kramer et al . 1997). Metal bioaccumulation by plants depends on pH, temperature and dissolved ions in water (Engin et al . 2015). Crews and Davies (1985) grew six different lettuce species in soils contaminated with various concentrations of metals Cd, Cu, Pb, and Zn and the uptake of Cd and Zn increased with increasing concentration in the soil and there was a significant correlation for accumulation of both metals in lettuce leaves. A quaponics is a promising, environmentally friendly and sustainable technology that contributes to food security and has the potential to alleviate poverty in many developing countries. Aquaponics technology consists of a recirculating water system where raising aquatic food animals (aquaculture) is combined with soilless growth of plant food crops (hydroponics). Fish and plants interact in a symbiotic manner, where fish provide nutrients for plants and in turn plants filter water to improve water quality conditions for fish. Water evaporation and transpiration by plants can lead to concentration of salts and heavy metals in the system. This would be problematic if metals and metalloids become concentrated to the point where they exceed MaximumContaminant Levels (MCLs) set by the USEPA for potable water quality. Developing countries tend to have higher concentrations of heavy metals in water supplies than developed countries (Jarup 2003) and thus, aquaponics systems are potentially more at risk of heavy metal contamination in developing countries. Heavy metal contamination of fish and vegetables could present risks to human health. Heavy Metals Heavy metals such as Cd, Pb, Hg, and As can threaten the sustainability of aquaponic systems (FAO 2014) because heavy metals may become toxic for living organisms, including bacteria that aid in nutrient cycling in aquaponic systems (Has-Schon et al . 2006, Schenone et al . 2014, Saha et al . 2015). Heavy metals are considered pollutants due to their toxicity, persistence in the environment and their ability to integrate and in some cases bioaccumulate within food chains (Klavins et al . 2000, Armitage et al . 2007, Sakan et al . 2009). Heavy metals can accumulate in fresh and marine water systems (Mendiguchia et al . 2006, Salami et al . 2008), posing a potential health concern for consumers and possibly leading to financial losses if concentrations in water exceed MCLs. Moreover, uptake of heavy metal contaminants may lead to concentrations in fish or edible plant tissue that exceed standards, contributing to economic losses, environmental degradation and negative human health impacts. Accumulation of Heavy Metals Heavy metals are used in many common agriculture and aquaculture practices as necessary micronutrients; metals are often added to animal feed, inorganic or organic fertilizers and pesticides, leading to increased heavy metal concentrations in the environment Accumulation of Heavy Metals and their Effects on Antibiotic Resistance of Bacteria in an Aquaponics System Hany M. Almotairy, Kevin Fitzsimmons and Jean E. McLain ( C O N T I N U E D O N P A G E 5 4 ) Water evaporation and transpiration by plants can lead to concentration of salts and heavy metals in aquaponics systems. Developing countries tend to have higher concentrations of heavy metals in water supplies than developed countries and thus, aquaponics systems are potentially more at risk of heavy metal contamination in developing countries. Heavy metal contamination of fish and vegetables could present risks to human health.