Replacing fish meal by food waste to produce lower trophic level fish containing acceptable levels of polycyclic aromatic hydrocarbons: Health risk assessments
Introduction
Polycyclic aromatic hydrocarbons (PAHs) are well-documented class of contaminants found in water and sediments, and are an environmental concern as they are toxic, long-lived, and can travel long distances (Neff, 1979, UNEP, 2005). PAHs are a large group of compounds composed of two or more fused aromatic rings, with more than 100 congeners. They are byproducts of incomplete combustion of organic materials, which are usually deposited in soils and sediments of aquatic systems, through petroleum contamination, fallout from air pollution, and terrestrial runoff (Christensen et al., 1997, Yang, 2000). Due to their carcinogenic properties and acute toxicity, 16 congeners of PAHs have been listed as priority control pollutants by the USEPA (USEPA, 2014). These compounds have extremely strong bonds between their chlorine and carbon components and are attracted to fat and highly insoluble in water. Therefore, they possess chronic toxicity, persistency, and bioaccumulative ability (Fisk et al., 2001, Hop et al., 2002), and are also endocrine disrupting chemicals (Li et al., 2008, Soto et al., 1995). The PAHs could contaminate pond sediments through irrigation and atmospheric deposition over a long period, subsequently entering into food chains, accumulating in fish, and finally reaching humans. Most of the studies related to health risk assessment of environmental chemicals in fish have been targeting dioxins, organochlorinated pesticides (OCPs) and polychlorinated biphenyls (PCBs) (Cheung et al., 2007, Hites et al., 2004, Xing et al., 2008), however, few studies focus on PAHs (Wang et al., 2010).
Food waste is a global problem that impacts the environment and society. When food waste is disposed to the landfill, it would rot quickly, and produce substantial quantities of methane gas which is a potent greenhouse gas with 25 times the global warming potential of carbon dioxide (Hall et al., 2009). The food processing and transportation also consume large quantities of fresh water and fossil fuels. In the U.S., it has been noted that, on average, 27% of all edible food goes to waste (USEPA, 2012). The amount of food wastes generated in Hong Kong has increased in recent years. In 2011, food waste comprised of one-third (about 330,000 tonnes) of the MSW loads at landfills (about 900,000 tonnes) (EPD, 2011). In Hong Kong, the remaining capacities of the three existing landfills will be exhausted by 2018 (EPD, 2011). In order to reduce the loading of local landfills, the policy framework of the Hong Kong Government on Municipal Solid Waste Management (2005–2014) mainly focused on waste reduction through producer responsibility schemes, waste charging and landfill disposal bans. In addition, the reuse, recovery, and recycling of wastes have been strongly advocated (EPD, 2005).
Fish meal is commonly used in aquaculture as a nutrient rich protein supplement ingredient (Kaushik et al., 2004). Most fish meal is derived from trash fish which are small fish or fragmented fish tissues collected from capture fisheries, with a low economic value. Pollutants can be accumulated in trash fish. It has been demonstrated that the use of trash fish as fish feeds was more polluted than using pellet feeds, based on the concentrations of persistent organic pollutants (POPs) such as OCPs, bromated flame retardants (PBDEs) and PCBs (Guo et al., 2009). In addition, our previous studies also showed that trash fish used in Pearl River Delta (PRD) contained higher levels of Hg than pellet feeds (Cheng et al., 2011, Liang et al., 2011). In European counties, fish meal derived from the trash fish for production of pellet feeds also contained high concentrations of PBDEs, perfluorinated compounds, dioxin/furans and PCBs (Suominen et al., 2011). Therefore, the use of trash fish as fish feeds and as ingredients of fish meal for producing pellet feeds is the major source of pollution worldwide.
It is hypothesized that food waste can replace part of the fish meal used in fish feeds to produce quality fish. The major objectives of the present study were to address the questions of whether: (1) the food waste fish feeds can provide necessary nutrients for fish growth; (2) using food waste feed would affect PAHs concentration in the ponds; (3) the cultured fish would accumulate higher levels of PAHs leading to biomagnification through food chains; and (4) consumption of the cultured fish would exert any potential health risks to Hong Kong residents. The basic data were shared among different members, and Table 1 was derived from Mo et al. (2014).
Section snippets
Experiment design
The experimental design followed the method described by our prior works (Mo et al., 2014). In this study, the traditional fish farming model used to culture low trophic level fish (all imported from mainland China) include: filter feeders (bighead, Hypophthalmichthys nobilis [10–12 cm]), herbivores (grass carp, Ctenopharyngodon idellus [13–16 cm]), and bottom feeders (mud carp, Cirrhinus molitorella [4–6 cm]) of omnivorous chain. Grass carp mainly consumes macrophytes, and also feed pellets.
Fish feeds
According to Table 1, the values of length, weight, feed conversion ratio, specific growth rate, and protein efficiency ratio in grass carp in Sha Tau Kok fish ponds, fed with FW A were significantly higher than those fed with FW B (p < 0.05), and similar to those fed with control diet (p > 0.05). Cereal food waste was used as the major protein source of FW A (53%), and meat waste was used to replace parts of cereals (25%) in FW B, and also used as major ingredient (28%) in FW B which were similar
Conclusions
The analyses of PAHs in various food waste ingredients showed that fruits, vegetables and bone meal were the major sources of PAHs, while meat products also contributed a significant source of PAHs for manufacturing fish pellets (FW A and FW B). No significant differences (p > 0.05) in PAHs were observed in water, SPM and sediment among the 3 experimental fish ponds. The results indicated that pond sediment might accumulate more PAHs, due to the use of more fish feeds to culture fish in the 2nd
Acknowledgment
Financial support from the Environmental and Conservation Fund (37/2009), Seed Collaborative Research Fund from the State Key Laboratory in Marine Pollution (SCRF0003), the Scientific Research Foundation of Sichuan agricultural university (01427800) and Special Equipment Grant (SEG, HKBU 09) of the Research Grants Council of Hong Kong are gratefully acknowledged.
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2017, Science of the Total EnvironmentCitation Excerpt :Due to the scarcity of scientific literature on this topic, our results are difficult to interpret, and obviously more research is needed. As stated above, a dietary intervention on the fish feed would be helpful to controlling the level of organic residues found in the final products, also in the case of emerging pollutants (Bethune et al., 2006; Cheng et al., 2015). The findings of this study reveal that the levels of pollutants vary in bogues according to the site of capture.
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