As non-essential metal, Cd is highly dangerous because is readily accumulated in aquatic animal cells and is not prone to bacterial detoxification (Jarup et al. 1998). The main source of Cd in many marine invertebrates is food and the ease with which these animals assimilate this contaminant from their prey (Chiarelli and Roccheri 2014). It seems that the crustaceans, in particularly, accumulate Cd from water without significant excretion, storing this element in detoxified form (Rainbow and White 1989). In addition, some environmental factors such as salinity, temperature and calcium concentration may also influence Cd toxicity (De Lisle et al. 1988).
In particular, crustaceans seem to be more sensitive to cadmium than fish and mollusks (Sadiq 1992). Previous studies regarding the effects of Cd on the ovarian development of crabs and shrimps showed that this metal inhibits ovarian growth, reduces the rate of fertilized eggs hatching, as well as embryonic deformity (Kang et al. 2012).Cadmium concentrations are relatively higher in muscle than in P. edwardsii eggs, thus confirming the importance of contamination through the benthic prey ingestion that colonize the homogeneous sediments (vase). Indeed, the Cd concentration in the sediment of the west coast of Gulf Annaba is estimated around at 1.5 mg.Kg–1 dry weight (Ouali et al. 2018).
Since this species is fished in deep waters, between 250 and 380 m along the east coast of Algeria (Fischer et al. 1987), the concentrations of Cd obtained in the muscle assume that the dispersion of Cd in the Gulf of Annaba extends beyond from coastal area probably through the geochemical process. On the other hand, the low concentrations of Cd accumulated in the eggs which are fixed under the abdomen of the females of P. edwardsii could be explained by the molting phenomenon which allows the females to get rid of their shell after each exuviation. In Annaba Gulf, ovigerous females are observed all year except in December (Oudainia, personal data not communicated), as commonly seen the Mediterranean coasts (Colloca 2002; Possenti et al. 2007).
In autumn, Abdennour et al. (2000) found in Penaeid shrimp Parapenaeus longirostris and Aristeus antennatus caught in the same study area (Annaba Gulf), concentrations of 0.61 and 0.78 µg.g-1 respectively. In Bejaia and Jijel Gulfs (East Algeria), Ghorab and Khebbeb (2012) found significantly higher cadmium concentrations in muscle tissue of males compared to females in two Peneidae (A. antennatus and P. longirostris) and a Caridae species (Palaemon serratus). In Plesionika martia and P. edwardsii sampled on the Turkish coasts between 450 - 500 m, Olgunoğlu (2015) found values below detectable limit. Rao et al. (2016) determine in three Caridae shrimp (Acanthephyra armata, Heterocarpus gibbosus and Plesionika spinipes) caught in the waters off the west and east coasts of India (depth: 200 - 1200 m), concentrations below the detectable limit. These negligible values of Cd in the muscle of these species would be explained by the absence/or low dispersion of this contaminant by seawater currents in deep waters in these study areas, hence the low accumulation of this metal in muscle tissue.
However, these low levels do not exclude the risk of bioaccumulation in these crustaceans, which are known to be bioaccumulative species. These values did not exceed the permissible limits of 0.2 mg.kg-1 WHO (1989) (Table 3).
Moreover, Cd levels in the studied samples were lower the risk international standard (0.05-2 with an average value of 0.3 mg.kg-1 wet weight) presented by FAO for Reference Dose, and do not pose any health risk to consumer. World Health Organization (WHO 2000) recommends a maximum tolerable weekly intake of cadmium (7 μg.kg-1 body weight per week).
Although Pb is a naturally occurring substance, this element is a very reactive in the environment whose the atmosphere represents its main vector towards sea and oceans. In decapod crustaceans (crabs and shrimps), the accumulation of Pd varied according to the geographical site. These invertebrate organisms can be considered as biomarkers of pollution by Pb (Mansoori et al. 2013). Using the experimental radiotracer method, Boisson et al. (2003) noted that the muscles of Palaemonetes varians shrimp could accumulate approximately 23 to 27% of Pb after ingestion of contaminated food. Therefore, the food pathway is suggested to be a significant contributor to the lead transfer to humans through ingestion of contaminated shrimp.
The high concentrations of lead in P. edwardsii indicate that the decapods are net accumulators of this element (Rainbow 1989). The high concentration of Pb in the muscle and eggs of P. edwardsii females is certainly of anthropogenic origin. Indeed, the Gulf of Annaba receives many sources of pollution: domestic (discharge of wastewater), agricultural and industrial through the water transported by Meboudja and Seybouse Rivers. With a watershed of 6471 Km² and an annual volume of 950.106 m3 of fresh water discharged into the Gulf (Ziouch et al. 2020), the Seybouse River is one of the largest watersheds in Algeria which discharges its polluted waters in the Gulf of Annaba, without prior treatment (Belabed et al. 2013).
On the other hand, the waters of Annaba port, highly enriched in metallic contaminants, communicate directly with the waters of the Gulf. This metallic pollution is at the partly origin from terminals of the coal and iron ore and steel products from the Arcelor-Mittal industrial complex, e.g. ISPAT. In addition, the highest lead and copper contents are recorded in the two Annaba commercial and fishing ports (Ouali et al. 2008). This situation would be due to the use of anti-fouling paint in the covering of boat hulls as well as from road traffic atmospheric emissions. Generally, the lead would affect not only the water and sediment compartments (Belabed 2010), but also the biota compartment of the Gulf soft bottoms, in particular macrozoobenthic species. In reality, metallic contamination by Pb is not limited to the area bordering on the pollutant source, but can extend to all of the Gulf waters through biogeochemical, physico-chemical and biological phenomena.
According to Belabed (2010), Pb is present in the sediment of the peri-urban area of the coast at high concentrations, up to 186 mg.kg-1 dry weight near the port (Sidi Salem Beach) explaining the high concentrations of this element in the muscle and eggs of P. edwardsii. In autumn, Abdennour et al. (2000) found in Peneidae shrimp P. longirostris and A. antennatus caught in the same study area (Annaba Gulf), concentrations of 2.3 and 1.1 mg.kg-1, respectively. On the other hand, in the Bejaia and de Jijel Gulfs, Ghorab and Khebbeb (2012) specify that P. serratus accumulates more lead than A. antennatus and P. longirostris, respectively. In the muscle of the same species A. antennatus from the Oran Gulf (West Algeria), Terbeche (2006) found a low concentration in spring (0.414 ppm) and autumn (0.290 ppm), appearing in the following decreasing order to Pb>Cd.
The World Health Organization prescribes that maximum tolerable limit weekly intake for lead as 25 µg.kg-1bw (WHO 2000). These values highly exceeded the permissible limits set by WHO (1984) (< 2 mg.kg-1). Moreover lead levels in the studied tissues were above the risk international standards (0.5-10 mg.kg-1 w.w.t).
Regarding copper, it is an abundant element which occurs as a natural mineral with a wide spread use. Toxicity towards marine organisms depends on the chemical form of this element and its oxidation state. In the decapod crustaceans, it represents as essential trace element, because their hemolymph contains a cooper-based respiratory pigment, called hemocyanin, serving as oxygen carrier. Everaarts and Nieuwenhuize (1995) reported that crustaceans could resist to Cu level of 140 mg.kg-1 comparatively to annelids and mollusks. Generally, decapods have the biological capacity to regulate this metal and keep it at a relatively constant threshold. In the Gulf of Annaba, even if Cu concentrations in the sediment reach values between 60 and 90 mg.kg-1 dry weight near the port (Belabed 2010), the estimated mean level of Cu in muscle tissues of females and males as well as in P. edwardsii eggs remains low, 1.137, 0.597, 0.718 mg.kg-1, respectively.
Despite the presence of industrial activities along the Annaba coast (waste from the Fertial and Arcelor-Mittal industrial complexes) and the importance of domestic discharges and nutrient-enriched waters discharging into the Gulf through the Meboudja, Seybouse and Mafragh Rivers (Belabed 2010), Cu was present at low concentration in the studied tissues with no significant differences between males and females in four seasons. However, these low levels, especially in muscle tissue, do not exclude the risk of bioaccumulation in these crustaceans which are known to be bioaccumulative species.
In other Penaeid shrimps of economic interest caught along the east coasts of Algeria, particularly in P. longirostris and A. antennatus, Abdennour et al. (2000) found in muscle tissue respectively concentrations of 114 and 139 µg.g-1. Out a total of 8 quantified trace metals (K, Na, P, Ca, Mg, Fe, Zn, Cu, Mn) in muscle tissue of Penaeid shrimp F. merguiensis from Persian Gulf (Iran), Baboli and Velayatzadeh (2013) found value of 1.26 (±0.2) µg.g-1 dry weight for the copper. Under experimental conditions, the white-legged shrimp, Litopenaeus vannamei exposed to a copper concentration of 0.35 mg.L-1 for more than 9 weeks, underwent structural changes in the hepatopancreas with melanization of the gills, thereby affecting the growth, molting and survival rate (Cheng et al. 2014). In Macrobrachium rosenbergii, Penaeus monodon and L. vannamei species, the Cu concentration of 0.089 mg.L-1 is considered as safe (Cheng et al. 2014). In P. martia and P. edwardsii sampled on the Turkish coasts between 450 - 500 m, Olgunoğlu (2015) found respectively values 1.357 (±0.01) and 2.04 (±0.01) mg.Kg-1. In muscle tissue to three Caridae shrimp (A. armata, H. gibbosus and P. spinipes) caught in the waters off the west coasts of India, Rao et al. (2016) have found respective following concentrations: 22.28 (±0.03), 7.15 (±1.56) and 29.8 (±4.30) µg.g-1. In the western sector of the same area, these same authors found different concentrations: 33.92 (±7.38), 4.11 (±0.79) and 12.65 (±0.79) µg.g-1.
In our work, the obtained values are considered lower than the International Standard set by WHO (1996). In addition these results did not exceed the permissible limits suggested by the Food and Agricultural Organization (FAO 1983), being 30 mg.Kg-1.
After iron, and copper, zinc is the third transition metal and the most developed by human. This trace metal is essential to life of a large number of organisms since it is involved in many physiological processes as enzymatic reactions and metabolism of proteins, carbohydrates and lipids. At low concentration, it causes various tissue lesions, delays growth and disrupts reproduction particularly in aquatic invertebrates and vertebrates (Ramade 2000). Zinc concentrations in P. edwardsii shrimp are within the ranges reported in other decapod species (Abdenour et al. 2000).The anthropogenic contributions of zinc in Annaba gulf is thought to be the cause of industrial sources (ores, refinings, galvanization of iron), agricultural (animal feed, phytosanitary products use), urban (road traffic, incineration) and port activities (anti-fouling paints).
Zinc concentrations measured in the studied tissues did not exceed the risk international standards set by United Nations Food and Agriculture Organization for reference doses, which reported that Zn level should be in the range of 40-100 ppm with average value of about 50 ppm wet weight. More over Zn concentration in this study is below permissible level for marine seafood (100 ppm) (WHO 1989).
Iron is an essential bio-metal for many living organisms because it is involved in many physiological and metabolic processes in humans and animals such as oxygen transport, the synthesis of enzymes being involved in cellular respiration, as well as the synthesis of DNA and cofactors (Caiguo 2014). Iron is present in low concentration in marine water compared to fresh water; this is linked to its chemical characteristics. In fact, in seawater, iron takes the form of Fe+3 whose the solubility is very low (Stummand Morgan 1996). Toxicity of this metal to fish and crustaceans depends on pH and the deposition of ferric hydroxide on gills (Peuranen et al. 1994).The female shrimp P. edwardsii showed a high level of metallic trace elements compared to the male, practically throughout the year. In the Mediterranean Sea, ovigerous females of P. edwardsii were observed throughout the year, exhibinting a peak of spawning activity between April and July (Company and Sarda 1997; Colloca 2002). This difference in metallic accumulation is relative to the reproduction physiology of this species. During the reproduction period, gametogenesis is characterized by the increased accumulation of metallic trace elements (Zn, Cu, Fr) necessary for vitellogenesis. This period corresponds to a phase of gametogenesis being characterized by an increased accumulation of reserves and a synthesis and storage of carbohydrate, lipid and protein material.
Urban, agricultural and industrial discharges are the source of iron at sea through the Seybouse and Meboudja Rivers. High concentrations of Fe have been displayed in Meboudja River downstream from the Arcelor-Mittal steel complex discharges (liquids, dust emissions), located 10 kilometers south of Annaba gulf. Additionally, the iron discharges also come from the open marketing of iron ore and its derivatives in the form of particles in the commercial port of Annaba. The dissemination of this metal in the marine environment is favored both by the direction of the prevailing winds (from west to east) which transport ferrous products in the form of dust, produced by the steel factory towards the sea and, hydrodynamically of the Gulf which receives the North East currents (Belabed 2010). Discharges into the sea from the Arcelor-Mittal industrial complex present many iron-rich chemical pollutants, mainly due to alloys used in industry (steelworks), being estimated at 1390 mg/L (Boughrira 2015).
The FAO/WHO (1999) regulation limits for heavy metals consumption are based on body weight. For an average adult (60-Kg body weight), the FAO/WHO (1999) suggests 48 mg as the provisional tolerable daily intake for iron. Although the requirement levels of this metal from diet absorption necessary for human physiological activities are not distinctly determined.