Contaminants in aquaculture: Overview of analytical techniques for their determination

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Highlights

  • The determination of contaminants in the aquaculture samples is crucial for controlling food safety hazards.

  • The contaminants can enter the aquaculture systems mainly via feed and are subsequently transferred to organisms.

  • The analytical techniques for the aquaculture contaminants have been discussed.

  • The major contaminants are polychlorinated biphenyls (PCBs), organochlorinated pesticides (OCPs) and antibiotics.

Abstract

Increasing attention has been focused on the presence of contaminants (e.g., polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), organochlorinated pesticides (OCPs), potentially toxic elements, as well as residues of veterinary drugs and antibiotics) in aquaculture products (fish, crustaceans and molluscs). Such contaminants enter the aquaculture systems mainly via feed and then are transferred to organisms. A sensitive and reliable determination of contaminants in aquaculture samples become crucial for controlling food safety hazards, and the efficient assessment of extraction and clean-up methods is essential to contribute to the overall data quality.

This overview discusses the analytical techniques for the determination of contaminants in aquaculture, which could interfere with the food safety of produced organisms such as fish, crustaceans and molluscs. The comparison of the concentrations of the contaminants found in the aquaculture products with those established in the global or the European legislations for foodstuffs is also considered. Finally, future perspectives on the determination of aquaculture contaminants are also proposed.

Introduction

Aquaculture is one of the pillars of the European Union Blue Growth Strategy and its development can contribute to the Europe 2020 Strategy [1]. The aquaculture is defined as the rearing or cultivation of aquatic organisms using techniques designed to increase the production of those organisms beyond the natural capacity of the environment [2]. Aquaculture is also known as fish and shellfish farming under controlled conditions in marine or freshwater environments. Marine aquaculture usually occurs in cages on the seafloor or suspended in the water column, and the species most produced are oysters, clams, mussels, shrimp and salmon; freshwater aquaculture usually occurs in ponds or recirculating aquaculture tanks, and the species most produced are catfish, trout, tilapia and bass [3].

According to the last issue of ‘The State of World Fisheries and Aquaculture’ published by the Food and Agricultural Organization of the United Nations [4], the aquaculture is continuing its impressive growth, in both increased quantity and improved quality. The world aquaculture production attained 90.4 million tons in 2012 including 66.6 million tons of food fish (e.g., finfishes, crustaceans, molluscs and amphibians) for human consumption [4]. The world food fish aquaculture production has continuously increased from approximately 13 million tons in 1990 to 32 million tons in 2000 and to 67 million tons in 2012 [4]. The average annual rate for the aquaculture production has increased from 5.7% in 2008 to 6.9% in 2012 [4]. Higher production is observed in Asian countries with 88.4% in 2012, where China alone accounted for 61.7% of the total production; Europe accounted 4.3% of the total global aquaculture production in 2012 [4]. The main species produced in European aquaculture in terms of weight (in 2011) are mussels (mainly Mytilus galloprovincialis and Mytilus edulis, 456,000 tons, 36% of the total EU (European Union) production), rainbow trout (mainly Onchorynchus mykiss, 179,000 tons, 14% of the total EU production), Atlantic salmon (mainly Salmo salar, 171,000 tons, 13% of the total EU production), Pacific cupper oysters (mainly Crassistrea gigas and Ostrea edulis, 104,000 tons, 8% of the total EU production), gilthead sea bream (Sparus aurata, 99,000 tons, 8% of the total EU production), European sea bass (Dicentrarchus labrax, 73,000 tons, 6% of the total EU production) and common carp (Cyprinus carpio, 62000 tons, 5% of the total EU production) [5].

The aquaculture production can be developed in extensive or intensive systems, according to the respective low or higher fish density. In extensive systems, organisms grow in lagoons or brackish waters naturally fed, while in intensive systems, they are bred in tanks and fed with special feeds according to each single species; the semi-intensive systems can also occur when the natural diet is supplemented with special feeds [6].

The main objective of aquaculture is the production of high nutritional value foods for human consumption. However, apart from its valuable food supply and economic support for many countries, the aquaculture practice can cause environmental problems such as pollution of the surrounding waters with nutrients, solid wastes and chemicals (e.g., antibiotics) that are used for disease control in the aquaculture tanks. Regarding chemical contaminants (concentration and duration of exposure), the ingredients of commercial animal feeds can be responsible for food safety risks in aquaculture; the major animal feed contaminants reported are veterinary drug residues, persistent organic pollutants, pesticides, metals and mineral salts (mercury, lead, cadmium, hexavalent chromium, arsenic and selenium) [7]. The typology of feeds and the quality of waters can be considered to be important critical factors in fish farming [8]. The exchanges between fish body, water and food can be described by uptake via food and water, and losses via metabolism, growth dilution, egestion and gills [9]. The contaminants present in aquaculture, whether intentionally or unintentionally, can be metabolized and excreted (such as veterinary drugs), detected at residual levels, or accumulated in fish. The bioaccumulation of toxic contaminants by farmed fish, bivalves, crustaceans and molluscs becomes a serious environmental problem mainly related to human supply. As stated by the European Food Safety Authority [10] and Håstein et al. [11], the contaminant concentration in farmed fish and shellfish depends on various factors such as the species, the capture season, the origin, the development state, and the tissue, and the levels vary within species and between species in both wild and farmed fish [10]. Comparative studies have demonstrated that man-made contaminants such as pesticides, polybrominated biphenyl ethers (PBDE) and polychlorinated biphenyls (PCB) were found at higher concentrations in farmed fish than in wild fish (salmon, catfish, turbot and sea bass) [12], but there is a need for the standardization of sampling procedures before a robust comparison of wild and farmed fish can be made [10].

The sample preparation is an important step in the analysis of contaminants from environmental samples due to the occurrence of matrix effects which are directly associated with the complexity of such environmental matrices [13]. Regarding the determination of contaminants in aquaculture matrices, it is well known that such matrices are complex and the large amounts of fat and other interfering substances present are co-extracted with the analytes of interest. Thus, the choice of the extraction method or combination of extraction methods together with the clean-up procedures should be well defined to obtain extracts with minimal fat content for further efficient analysis of contaminants. The determination of contaminants in aquaculture is crucial to the control of food safety of the produced organisms. The organic enrichment of aquaculture waters from sediments is also an important topic, and the analysis of contaminants in water and sediments is also required for monitoring the water quality.

This study aims to review the state-of-the-art current analytical techniques published in the recent period of 2008–2015, which are used for the determination of contaminants, that is, polycyclic aromatic hydrocarbons (PAHs), brominated flame retardants (BFRs), PCBs, organochlorinated pesticides (OCPs), potentially toxic elements and residues of veterinary drugs and antibiotics, in various samples from aquaculture such as fish, crustaceans and molluscs. The occurrence of such contaminants in aquaculture and the analytical procedures required before analysis, such as extraction and clean-up, are also discussed.

Section snippets

Occurrence of contaminants in aquaculture

Aquaculture has been increasingly used to produce foodstuffs such as fish and shellfish and it has been strictly controlled by global and European regulations in order to define maximum levels of substances in such products. For example, the EC 1881/2006 regulated the maximum levels of contaminants such as metals (Pb, Hg and Cd) and PAHs in foodstuffs such as muscle of fish, crustaceans and bivalve molluscs [14]; the EC 1259/2011 regulated the maximum levels for dioxins, dioxin-like PCBs and

Sampling, extraction and clean-up methods

Table 1 displays results of the recent works on the determination of contaminants in aquaculture samples, where extraction and clean-up methods are also identified.

For the majority of the works reported in Table 1, the following procedures have been considered: a) fishes were collected from the aquaculture sites and transported alive to the laboratory in ziplock polyethylene bags or wrapped in an aluminium foil. b) Fishes were eviscerated and peeled and their edible tissues such as muscle,

Separation, detection and determination of contaminants in aquaculture

Various analytical techniques were suggested for the determination of contaminants in the aquaculture samples (Table 1). Liquid (LC) or gas chromatography (GC) with MS detection is proposed as a suitable confirmatory method for organic residues or contaminants in foodstuffs [65]. Effectively, approximately 54% of the works analysed in this review used the GC or LC combined with MS for the determination of organic compounds in fish or shellfish, as shown in Table 1. The GC–ECD (electron capture

Quality assurance and quality control

The representativeness is important for the reliability of analytical information. A representative sample is a sample that is typical of the parent material for the characteristics under inspection. The aquaculture samples taken into consideration in this review are associated with a very dynamic system, as the sample at any instant is characteristic of the sampling moment and in a particular location. Thus, the sampling plan should be well defined for identifying the exact geographic location

Conclusions and future perspectives

Although the aquaculture production has been increased both at a global state and in the European countries, constituting a valuable food supply and also promoting the economic development, potential contamination of the aquaculture products by animal feed, veterinary drugs and/or the neighbouring environmental conditions of aquaculture sites still remains. Some works reported levels of contaminants higher than those established in global or European legislations, which should arouse further

Acknowledgements

This work was funded by the Portuguese Science Foundation (FCT) through scholarships (ref. SFRH/BPD/95961/2013, SFRH/BD/84524/2012 and SFRH/BPD/73781/2010) under POCH funds, co-financed by the European Social Fund and Portuguese National Funds from MEC. This work was also funded by national funds through FCT/MEC (PIDDAC) under project IF/00407/2013/CP1162/CT0023. Thanks are also due, for the financial support to CESAM (UID/AMB/50017), to FCT/MEC through national funds, and the co-funding by the

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