3.1. Content and composition of fatty acids
Total fat acids and subgroups including saturated fatty acids (SFAs), monounsaturated fatty acids (MUFAs), polyunsaturated fatty acids (PUFAs), omega-3 and omega-6 fatty acids in fish and shrimp species from Chaohu Lake were summarized in Table 1. Furthermore, the contribution of various subgroups to the total fatty acids and the mean percentage of DHA + EPA in omega-3 PUFAs for different species were depicted in Fig. 2. Total fatty acid contents in fish and shrimp species differed substantially with a mean range of 270.0-2107.5 mg/100g ww. Among species, lake anchovy (CoE) had the highest whereas icefish (NeT) had the lowest fatty acid content. Difference in fatty acid contents might be attributable to the lipid content in various species (Cui et al., 2018; Laird et al., 2018). SFAs, MUFAs, PUFAs contributed 21–28%, 26–55%, 19–48% to total fatty acids, respectively (Fig. 2a). Composition profile of fatty acids in studied species was similar to those species from Taihu Lake, another large eutrophic freshwater lake in China (Zhang et al., 2012a). It seemed MUFAs and PUFAs contributed more than SFAs to the total fatty acids. Divergence in composition of fatty acids might be related to a number of factors including species, feeding habit, ambient temperature, and life stage and age of the fish (Cui et al., 2018; Wang et al., 2020; Zhang et al., 2012a). Moreover, fish and shrimp species had favorable ratios of PUFA/SFA (all > 0.7), which was higher than the recommended nutritional guidelines (minimum value of 0.4–0.5, FAO/WHO, Neff et al., 2014). More importantly, health benefit of fat consumption was closely related to omega-6 and omega-3 PUFAs (Balshaw et al., 2012). Omege-6 PUFAs (e.g. linoleic acid) might counteract the beneficial effects of omega-3 PUFAs, thus the ratio of omega-6 to omega-3 PUFAs was an important nutritional quality index (Jing et al., 2021). The ratios were ranged from 0.4 to 0.9 (Table 1), which was comparable to the ratios reported for fish species from Taihu Lake (0.8–1.2, Zhang et al., 2012a) and much lower than four as recommended by FAO/WHO (Zhang et al., 2012a). Therefore, in view of content and composition of fatty acids, fish and shrimp species from Chaohu Lake were considered healthy food choices for human consumption.
Table 1
Mean content and composition of fatty acids (mg/100g ww) in fish and shrimp species collected from Chaohu Lake, China.
Species | FAs | SFAs | MUFAs | PUFAs | DHA + EPA | omega-3 | omega-6 | omega-6/omega-3 |
HyM | 857.7 | 207.2 | 339.8 | 305.8 | 113.8 | 192.6 | 86.1 | 0.4 |
ArN | 621.7 | 174.7 | 214.2 | 239.6 | 107.4 | 160.4 | 61.8 | 0.4 |
CyC | 371.7 | 86.3 | 107.4 | 178.0 | 84 | 102.9 | 66.2 | 0.6 |
CaA | 760.5 | 182.1 | 325.4 | 245.6 | 92.3 | 129.3 | 101.6 | 0.8 |
MeA | 882.9 | 187.6 | 384.1 | 307.0 | 96.2 | 164.9 | 132.3 | 0.8 |
CuA | 1337.6 | 335.1 | 590.8 | 400.4 | 154.6 | 224.7 | 149.0 | 0.7 |
HeM | 545.9 | 130.7 | 228.0 | 183.8 | 82.2 | 110.0 | 64.8 | 0.6 |
NeT | 270.0 | 76.9 | 73.6 | 117.3 | 70.4 | 77.6 | 32.8 | 0.4 |
CoE | 2107.5 | 548.4 | 1151.0 | 390.2 | 123.2 | 195.1 | 179.9 | 0.9 |
PaM | 731.1 | 190.1 | 186.5 | 349.3 | 184.3 | 226.8 | 114.4 | 0.5 |
MaN | 1140.4 | 237.9 | 510.9 | 384.9 | 185.3 | 248.1 | 123.7 | 0.5 |
HyM - Hypophthalmichthys molitrix; ArN - Aristichthys nobilis; CyC - Cyprinus carpio; CaA - Carassius auratus; MeA - Megalobrama amblycephala; CuA - Culter alburnus; HeM - Hemibarbus maculates; NeT - Neosalanx taihuensis; CoE - Coilia ectenes; PaM - Palaemon modestus; MaN - Macrobrachium nipponense. FAs - fatty acids; SFAs - saturated fatty acids; MUFAs - monounsaturated fatty acids; PUFAs - polyunsaturated fatty acids. |
Contents of DHA and EPA were the main factor when evaluating the health benefit through fish consumption (Du et al., 2012; Geng et al., 2015). However, data on DHA and EPA content in freshwater fish from China were scarce (Jing et al., 2021; Zhang et al., 2012a, b). Herein, the EPA + DHA contents were 29.0-238.6 mg/100g ww, covering a percentage of 5–31% in total fatty acids and 49–96% in omega-3 PUFAs (Fig. 2b), among which the highest mean value was found in shrimps Macrobrachium nipponense (185.3 mg/100g) and Palaemon modestus (184.3 mg/100g) whereas the highest percentage was discovered in icefish (NeT), though total FAs for this boneless specie was least but it was abundant in calcium and protein that was much suitable for children. Therefore, greater nutritional values in above-mentioned species enabled them to be identified as optimum choice for human consumption (Balshaw et al., 2012).
When setting those shrimp species aside, it could be found that greater content of omega-3 PUFAs was found in carnivorous topmouth culter (Table 1). It was speculated that feeding habits might be one of the main factors influencing the fatty acid composition (Zhang et al., 2012b). Omnivorous and herbivorous fish were devoted to elongate and desaturate those algae or plants synthesized short chain fatty acids to long chain fatty acids. Further, carnivorous fish, which scavenged on other fish species with no need for chain elongation and desaturation, were typically rich in omega-3 PUFAs (Inhamuns and Franco, 2008). In eutrophic lakes, phytoplankton communities changed and decreased essential fatty acids that eventually affecting the composition of fatty acids in higher trophic level species (Jing et al., 2021; Sardenne et al., 2020). However, Laird et al. (2018) and Wang et al. (2020) deemed that phytoplankton contained high levels of omega-3 PUFAs therefore leading to greater omega-3 PUFAs in omnivorous and planktivorous fish, whereas Kainz et al. (2017) demonstrated that the contents of omega-3 PUFAs were related to total lipid in freshwater fish regardless of feeding sources and trophic positions. Therefore, the reason for discrepancy in fatty acid composition was disputed and needed further research.
The total fatty acids content in present study (1.04–24.05 mg/g) was within the reported ranges of previous studies (Table S2), i.e. 2.3–3.9 mg/g for freshwater fish from Taihu Lake, China (Zhang et al., 2012a), 13.2–18.1 mg/g for market sold fish from Shanghai, China (Geng et al., 2015), 3.5–7.81 mg/g for freshwater fish from Lake Erie (Neff et al., 2014), and 2.6–87 mg/g for marine fish from the Bohai coast, China (Cui et al., 2018). More data was recorded for DHA, EPA, or DHA + EPA throughout the world. The DHA + EPA content in wild fish in present study were comparable to those from Taihu Lake, China (Zhang et al., 2012a), WJD Reservoir, China (Jing et al., 2021), market sold freshwater fish (Du et al., 2012), boreal lakes, Finland (Strandberg et al., 2016), whereas lower than those from the Dehcho Region (Laird et al., 2018), Lake Erie (Neff et al., 2014) and those from marine environment including the Bohai coast, China (Cui et al., 2018), the Portuguese coast (Cardoso et al., 2015), and New Zealand waters (Cressey et al., 2020). Contents of DHA and EPA tended to be greater in marine oily fish than in freshwater lean fish (Du et al., 2012; Geng et al., 2015). Even so, freshwater fish contained much less fat than most livestock meat (Lescord et al., 2020), thus freshwater fish was healthier alternative food with regard to less fat content as well as low environmental contaminants compared with seafood.
3.2. Content of essential and non-essential trace elements
Statistical description of essential and non-essential trace elements in the studied fish and shrimp species from Chaohu Lake were presented in Table 2. For essential trace elements, Fe was characteristic of the highest mean content being 10.3 µg/g, followed by Cu (9.9 µg/g), Zn (7.7 µg/g), Cr (1.42 µg/g), Se (0.337 µg/g), Mo (0.285 µg/g), I (0.023 µg/g). When in comparison with the maximum limits, it was found that Se content in more than half of the samples exceeded 0.3 µg/g (maximum tolerable level, Brazilian, Albuquerque et al., 2020) and Cr content in four samples was above 2 µg/g (GB 2762 − 2017, China). Indeed, the limit for Se was considered unrealistically low (Albuquerque et al., 2020). The non-essential As, Cd, Hg, Ni, Pb contents were in the range of nd-218, 14–97, 3–47, 4200–11300 and 144–1127 µg/kg, respectively, which was mostly below the maximum limits of the National Standard of China (GB 2762 − 2017) with the exception of Pb content in several samples. Overall, results revealed that non-essential trace elements were within a low content range in the majority of analyzed fish and shrimp samples from Chaohu Lake demonstrating a limited level of environmental exposure. In this case, trace element metabolism was considered to be regulated by homeostatic mechanisms, thus differences among fish species were related to physiological factors and feeding habits to a large extent (Albuquerque et al., 2020; Varol and Sünbül, 2018).
Table 2
Descriptive statistics of trace elements (mean ± sd) in different fish and shrimp species from Chaohu Lake, China (µg/g ww for Fe, I, Zn, Se, Cu, Mo, Cr; µg/kg ww for As, Cd, Hg, Ni, Pb).
Species | Fe | I | Zn | Se | Cu | Mo |
HyM | 10.8 ± 1.9 6.1–13.3 | 0.016 ± 0.003 0.009–0.026 | 5.6 ± 1.1 2.3–7.4 | 0.259 ± 0.076 0.027–0.416 | 10.3 ± 2.4 5.9–14.5 | 0.304 ± 0.056 0.207–0.386 |
ArN | 12.2 ± 1.7 8.8–14.5 | 0.019 ± 0.015 0.011–0.092 | 5.8 ± 1.1 2.9–7.4 | 0.309 ± 0.084 0.025-0.5 | 12.6 ± 3.5 5.9–17.5 | 0.342 ± 0.048 0.253–0.426 |
CyC | 9.3 ± 0.3 9.0-9.9 | 0.026 ± 0.004 0.021–0.033 | 13.0 ± 3.2 7.8–16.9 | 0.790 ± 0.298 0.530–1.244 | 5.3 ± 0.4 4.9–5.9 | 0.247 ± 0.006 0.238–0.258 |
CaA | 8.2 ± 0.9 6.4–9.1 | 0.032 ± 0.007 0.023–0.043 | 15.5 ± 3.0 11.0-19.4 | 0.459 ± 0.186 0.246–0.751 | 5.6 ± 0.3 5.2–6.2 | 0.229 ± 0.019 0.205–0.256 |
MeA | 8.1 ± 1.9 5.4–9.7 | 0.020 ± 0.003 0.018–0.024 | 5.5 ± 3.4 1.3-9.0 | 0.317 ± 0.244 0.004–0.593 | 7.2 ± 2.2 4.8–9.5 | 0.206 ± 0.023 0.178–0.229 |
CuA | 8.5 ± 1.0 6.0-9.6 | 0.018 ± 0.003 0.013–0.024 | 6.2 ± 0.8 5.2–7.8 | 0.423 ± 0.085 0.290–0.591 | 8.1 ± 0.9 7.2–9.7 | 0.190 ± 0.018 0.163–0.214 |
HeM | 9.2 | 0.012 | 8.6 | 0.471 | 8.7 | 0.186 |
NeT | 8.0 ± 2.0 5.8–9.7 | 0.059 ± 0.013 0.047–0.073 | 11.3 ± 3.2 7.6–13.2 | 0.297 ± 0.064 0.230–0.359 | 6.3 ± 2.4 4.7-9.0 | 0.275 ± 0.063 0.203–0.318 |
CoE | 8.3 ± 0.6 7.6–8.7 | 0.022 ± 0.008 0.015–0.030 | 14.9 ± 1.7 13.7–16.8 | 0.431 ± 0.171 0.290–0.621 | 7.8 ± 1.8 5.7-9.0 | 0.233 ± 0.050 0.201–0.291 |
PaM | 8.4 ± 1.3 7.0-9.5 | 0.078 ± 0.027 0.047–0.098 | 12.3 ± 0.4 11.9–12.7 | 0.291 ± 0.046 0.252–0.342 | 14.6 ± 1.0 13.6–15.7 | 0.269 ± 0.059 0.207–0.324 |
MaN | 6.8 ± 1.4 5.8–7.7 | 0.125 ± 0.004 0.122–0.128 | 32.0 ± 12.5 23.1–40.8 | 0.295 ± 0.020 0.281–0.309 | 16.9 ± 0.8 16.4–17.5 | 0.297 ± 0.018 0.284–0.310 |
maximum limit | 100 | | 30 | 0.3 | 30 | |
Species | Cr | As | Cd | Hg | Ni | Pb |
HyM | 1.43 ± 0.28 0.44–2.19 | 13 ± 6 nd-33 | 29 ± 10 14–67 | 7 ± 2 3–13 | 8443 ± 1446 4665–10286 | 249 ± 85 157–665 |
ArN | 1.48 ± 0.33 0.44–2.5 | 15 ± 9 3–42 | 27 ± 4 21–37 | 10 ± 5 5–25 | 9567 ± 1288 6863–11280 | 251 ± 84 167–651 |
CyC | 1.25 ± 0.07 1.12–1.35 | 6 ± 2 4–8 | 32 ± 7 25–44 | 26 ± 4 20–33 | 7324 ± 192 7230–7759 | 271 ± 111 249–521 |
CaA | 1.37 ± 0.21 1.13–1.70 | 14 ± 6 6–23 | 39 ± 26 25–97 | 28 ± 9 20–47 | 6465 ± 716 4984–7129 | 350 ± 343 208–1127 |
MeA | 1.23 ± 0.54 0.51–1.67 | 10 ± 10 2–24 | 34 ± 5 29–40 | 10 ± 5 5–17 | 6363 ± 1490 4238–7590 | 217 ± 52 144–265 |
CuA | 1.49 ± 0.23 1.02–1.87 | 12 ± 7 2–27 | 38 ± 8 28–49 | 18 ± 7 13–34 | 6630 ± 777 4759–7538 | 241 ± 57 181–372 |
HeM | 1.28 | 7 | 45 | 11 | 7279 | 226 |
NeT | 1.21 ± 0.37 0.85–1.60 | 14 ± 15 5–32 | 60 ± 17 43–77 | 9 ± 2 7–12 | 6296 ± 1678 4457–7744 | 276 ± 24 252–299 |
CoE | 1.58 ± 0.41 1.20–2.02 | 27 ± 16 14–45 | 48 ± 13 33–57 | 9 ± 1 9–10 | 6500 ± 399 6041–6765 | 330 ± 98 223–416 |
PaM | 1.29 ± 0.23 1.16–1.56 | 85 ± 47 44–137 | 53 ± 8 44–58 | 3 ± 1 3–4 | 6573 ± 1106 5344–7489 | 235 ± 33 214–272 |
MaN | 1.29 ± 0.17 1.18–1.41 | 165 ± 76 111–218 | 78 ± 18 65–90 | 4 ± 0 4-4.2 | 5145 ± 1167 4320–5970 | 268 ± 43 237–299 |
maximum limit | 2 | 100a | 100 | 500 | 70000–80000 | 500 |
a inorganic As; short names of fish species were same as in Table 1. |
Except for Macrobrachium nipponense, in which highest I, Zn, Cu, As, Cd and lowest Fe, Ni, Pb content was found, no obvious bioaccumulation pattern in individual species could be explored, which was different from previous studies that carnivorous and/or omnivorous fish was prone to accumulate more trace elements than planktivorous fish (Albuquerque et al., 2020; Jiang et al., 2018; Xia et al., 2019). Possible reasons for this discrepancy might be the limited sample size and relatively lower contamination level of trace elements in Chaohu Lake (Fang et al., 2017, 2019a, b). Accumulation of trace elements in fish was dependent on multiple factors including elemental type, trophic level, habitat, feeding habit, and ambient environment (Xia et al., 2019). Differences among fish species might be greater when fish was exposed to high environmental levels, which overloaded homeostatic mechanisms in fish (Albuquerque et al., 2020). Although no obvious bioaccumulation pattern was found among species, results of PCA analysis demonstrated that trace elements in fish and shrimp showed different accumulation tendency with various feeding habit and habitat (Fig. S1). It seemed that As, I, Cd, Zn, Pb, Se, Hg, and Cr was more accumulated in fish species living in the demersal layer or in fish species with higher trophic level, whereas the opposite trend was found for Cu, Mo, Fe, Ni. Therefore, non-essential elements in demersal or piscivorous species should be routinely monitored to ensure food safety.
Bioaccumulation of Hg in fish was closely related to the bioavailability of Hg (i.e. chemical speciation) in environment and the methylation efficiency of Hg to MeHg (Strandberg et al., 2016). Although Hg in water (Fang et al., 2019a) and sediment (He et al., 2016) was reported at levels of environmental concern in study region, Hg contents in fish and shrimp species from Chaohu Lake were much lower than the maximum limit of 500 µg/kg (GB 2762 − 2017, China) that suggested a low exposure across the aquatic ecosystem, which might be attributed to the low bioavailability of Hg in sediment (Fang et al., 2019a) and biodilution of cyanobacteria bloom (Strandberg et al., 2016). Mercury bioaccumulation in fish could be influenced by the structure of the planktonic food web (Signa et al., 2019). In eutrophic lakes, Hg was diluted as higher algal biomass, and low content at the base of the food web led to lower content at higher trophic levels (Strandberg et al., 2016). Besides, fat deposition might also contribute to dilute Hg already present in fish tissues (Cressey et al., 2020). Nevertheless, Jing et al. (2021) found higher Hg content in planktivorous fish in a eutrophic reservoir, which was a consequence of trophic transfer, i.e., planktivorous fish were mainly fed on plankton whereas other species on artificial fish food that experienced short time of Hg/MeHg exposure. Furthermore, fish and shrimp species from this study presented substantial Se content to countervail the toxic effects of Hg/MeHg exposure (Table 2).
Broad comparison was carried out with reported data in worldwide studies (Tables S2). Content of trace elements in fish and shrimp species from Chaohu Lake were within the same order of magnitude as previously reported data. It was noteworthy that Zn content in present study was higher than those quantified in fish from Western Pará (Albuquerque et al., 2020), Keban Dam Reservoir (Varol et al., 2018), northern Ontario (Lescord et al., 2020) and Nenets autonomous region (Sobolev et al., 2019), whereas lower than in fish from Taihu Lake, where denser industries were developed around the lake in past several decades (Fu et al., 2013). Similar to Zn, Cu was much higher in Chaohu aquatic species but close to it in Taihu fish species (Fu et al., 2013). Selenium contents in present study were comparable to those in previous studies, no matter focused on freshwater or marine fish (Lescord et al., 2020; Sobolev et al., 2019). Data for molybdenum was rare in previous publications (Albuquerque et al., 2020) meant this element was overlooked for its dietary intake through fish consumption. Herein, a higher accumulation for Cr and Ni was found, which might be related to the higher background levels in the Chaohu Lake catchment (Fang et al., 2019b; Liu et al., 2012b). Besides, Cd (14–97 µg/kg) and Pb (144–1127 µg/kg) in this study was much higher than farmed fish compiled from markets in big cities, China (Du et al., 2012; Geng et al., 2015). It was stated that farmed fish was fed on commercially formulated diets that reducing the bioaccumulation of toxic elements through trophic transfer (Du et al., 2012). The Hg content of fish and shrimp species in present study was much lower than previous studies, for example, those fishes from the Amazon region where was affected by mining exploitations (Albuquerque et al., 2020). Overall, accumulation of trace elements in freshwater fish was affected by both geographical condition and anthropogenic activities (Xia et al., 2019).
3.3. Relationship among length, fatty acids, and trace elements
Not only nutrients but also contaminants could be bioaccumulated to various degrees in different aquatic species, which was affected by multiple factors, such as the living environment, species, habitat, feeding habit as well as individual size (Cui et al., 2018; Grgec et al., 2020).
Significant positive correlations between total fatty acids and subgroups including SFAs, MUFAs, PUFAs, omega-3 and omega-6 fatty acids, and DHA + EPA were found (Table S3). In view of this, it was speculated fish increase or supplement fatty acids in equal proportions through food or other sources (Balshaw et al., 2012; Wang et al., 2020). The DHA + EPA were well correlated with total fatty acids (r = 0.711, p < 0.01), indicating that beneficial effects of fish consumption were closely associated with the fatness of fish (Neff et al., 2014; Strandberg et al., 2016). Furthermore, no significant correlation was found between the DHA + EPA contents in samples and habitats as well as feeding habits, which was consistent with previous study that PUFAs were adjusted as total lipid status regardless of feeding sources and trophic positions (Kainz et al., 2017). The relationship between fish length and fatty acids as well as subgroups was not investigated due to the composite samples of small-sized species included in FA analysis.
Correlation between fatty acids together with subgroups and trace elements were analyzed. Among trace elements, only Cu and As was positively correlated with fatty acids and subgroups, albeit the correlation was weak (r = 0.369–0.593, p < 0.05), indicating most of trace elements were lipophobic and more incorporated in proteins (Sobolev et al., 2019). Conversely, negative relationships were found between omega-3 fatty acids and Hg (p < 0.05), omega-6 fatty acids and Mo, Pb (p < 0.05), between DHA + EPA and Hg (p < 0.05). The negative correlation between fatty acids and Hg was sometimes discovered elsewhere (e.g. in Strandberg et al., 2016), indicating that the risk posed by toxic trace elements such as Hg could counteract the beneficial effects of essential fatty acids.
Accumulation levels tended to increase with fish size (Neff et al., 2014). Due to sample size, only Hypophthalmichthys molitrix (N = 56) and Aristichthys nobilis (N = 26) were chosen to investigate the effects of fish length and weight on bioaccumulation of trace elements at the species level. Results of Spearman rank correlation analysis were tabulated in Table S4. For Hypophthalmichthys molitrix, fish length and weight was significant factor for Fe, Cu, Mo, Hg, and Ni (p < 0.01), whereas for Aristichthys nobilis, it was positively associated with Cu (p < 0.01), Mo (p < 0.01), Cd (p < 0.05), Hg (p < 0.01), Pb (p < 0.05). Of note, Cu, Mo, and Hg were size-dependent in both species. Besides, negative association was found for As (p < 0.05) in ArN, indicating a dilution with growth and/or stronger detoxification and elimination mechanism of As in larger bighead fishes. Difference in the correlation result was probably related to their different dietary habits and homeostatic regulatory mechanism for trace element metabolism in each species (Albuquerque et al., 2020). Fish length and weight could be used as a basis for predicting those significantly correlated trace elements of individual fish (Cressey et al., 2020). Weak correlations among physiological factors and other trace elements suggested that fish physiological development was not main reason for the variation of these elements in individuals (Albuquerque et al., 2020).
Spearman rank correlation analysis was applied to explore the relationship between various trace elements within each species (Table S5). For HyM, significant positive correlations were found between Fe, Cu, Mo and Ni (p < 0.01), whereas strong negative association were discovered including Se-As and Cr-As (p < 0.01). And for ArN, significant positive correlations were found between Fe, Cu, Mo, Ni and Pb (either p < 0.01 or p < 0.05), whereas strong negative association were recorded between Cu, Mo, Ni and As (either p < 0.01 or p < 0.05). Strong correlation among trace elements reflected either approximate contamination degree or analogous pollution sources (Sobolev et al., 2019). Iodine, Se, and Pb displayed no association with other trace elements for both species, representing their divergent originations or metabolism mechanisms. Selenium was commonly considered to play an important role in Hg cycling and methylation (Grgec et al., 2020), however, in present study, no significant correlation was discovered between Hg and Se whereas the correlation was found between Hg and Cu, Mo, demonstrating that other essential elements might have the potential to relieve Hg toxicity in aquatic ecosystem (Albuquerque et al., 2020).
3.4. Benefit-risk assessment
Fish consumption and the related beneficial and hazardous effects differed to a large extent in specific areas, which was predominantly dependent on the composition of fish species and the amount of fish consumed (Du et al., 2012; Grgec et al., 2020). It should be kept in mind that the health benefit might be diminished by elevated content of environmental contaminants in aquatic species due to natural and anthropogenic activities that dispersing more contaminants into the aquatic ecosystems.
The beneficial effects of fish consumption were primarily ascribed to PUFAs, particularly DHA and EPA. According to the amount of fish and shrimp consumed to obtain enough DHA + EPA, efforts were made to assess the potentiality of fish and shrimp consumption to fulfill the daily requirement of essential trace elements in human body (Halder et al., 2020; WS/T 578.3–2017). To achieve the recommended 250 mg of DHA + EPA daily intake, the daily fish consumption ought to be 134.9-355.1 g (CREFA, Table 3). Therefore, on basis of the aforementioned amount, the contribution of fish consumption to the recommended daily intake of essential trace elements, i.e. RDI%, was calculated and shown in Table 3. It was found that fish and shrimp consumption could contribute 66–392%, 164–366%, 31–98%, 580–1432% to the recommended daily intake of Se, Cu, Mo, Cr, respectively. Therefore, it could be stated that fish and shrimp consumption to be considerable source of Se, Cu, Mo, and Cr for consumers, which was different from previous study that fish consumption was of little importance in nutrients intake except DHA and EPA (Du et al., 2012). On the other hand, more attention was paid to Cr for its rather high RDI%. It should be noted that Cr content in majority of the samples did not exceed the maximum limit (GB 2762 − 2017, China) with the exception that four samples had Cr content greater than 2 µg/g. However, Cr commonly existed in the trivalent state in natural foods that was non-toxic to human health (Lescord et al., 2020). Otherwise, the non-carcinogenic health effects of Cr was calculated (Table 3) and results showed the BRQNC for Cr was less than one signifying negligible health risk from Cr.
Table 3
Results of RDI% for essential trace elements calculated on basis of recommended daily intake in China (WS/T 578.3–2017).
Species | DHA + EPA mg/g | CREFA g/d | Fe | I | Zn | Se | Cu | Mo | Cr | BRQNCa |
RDI (mg/d) | 250 | 12 | 0.12 | 12.5 | 0.06 | 0.8 | 0.1 | 0.03 | |
HyM | 1.137 | 219.9 | 20% | 3% | 10% | 95% | 283% | 67% | 1048% | 0.003 |
ArN | 1.074 | 232.8 | 24% | 4% | 11% | 120% | 366% | 80% | 1148% | 0.004 |
CyC | 0.839 | 298 | 23% | 6% | 31% | 392% | 196% | 74% | 1242% | 0.004 |
CaA | 0.923 | 270.9 | 19% | 7% | 34% | 207% | 189% | 62% | 1237% | 0.004 |
MeA | 0.962 | 259.9 | 17% | 4% | 11% | 137% | 233% | 54% | 1065% | 0.004 |
CuA | 1.546 | 161.7 | 11% | 2% | 8% | 114% | 164% | 31% | 803% | 0.003 |
HeM | 0.822 | 304.1 | 23% | 3% | 21% | 239% | 331% | 57% | 1298% | 0.004 |
NeT | 0.704 | 355.1 | 24% | 17% | 32% | 176% | 277% | 98% | 1432% | 0.005 |
CoE | 1.233 | 202.8 | 14% | 4% | 24% | 146% | 197% | 47% | 1068% | 0.004 |
PaM | 1.843 | 135.6 | 10% | 9% | 13% | 66% | 248% | 36% | 583% | 0.002 |
MaN | 1.853 | 134.9 | 8% | 14% | 35% | 66% | 286% | 40% | 580% | 0.002 |
HyM | 1.137 | 219.9 | 20% | 3% | 10% | 95% | 283% | 67% | 1048% | 0.003 |
a BRQNC was calculated for Cr separately for its rather high RDI%. |
For non-essential trace elements, the BRQNC and BRQC values were calculated to determine the susceptibility of consumers to the non-carcinogenic and carcinogenic health effects through fish and shrimp consumption (Table 4). The BRQNC values for As, Cd, Hg, Ni, and Pb was in the range of 0.10–1.24, 0.10–0.36, 0.06–0.81, 0.58–1.86, and 0.13–0.41, respectively. Notably, eight out of the eleven fish and shrimp species had BRQNC values of Ni exceeded one, warning that consumers were at the risk of non-carcinogenic health effects of Ni. Besides, the BRQNC value of As for shrimp MaN had the value of 1.24 that was also larger than one. Due to the fact that only As had been provided the cancer slope factor (IRIS, US EPA), thus only the carcinogenic effect of As was evaluated herein. The BRQC values of As were ranged from 0.11 in CuA and HeM to 1.11 in MaN. It seemed that As in MaN shrimp might pose non-carcinogenic and carcinogenic risk on consumers. However, As was predominantly in non-toxic organic forms (e.g., arsenobetaine and arsenocholine) in aquatic species (Albuquerque et al., 2020; Gladyshev et al., 2020), in addition, the accumulation of Se might also decrease the As toxicity through antagonistic effect (Halder et al., 2020; Lescord et al., 2020), thus the concern on the deleterious effects of As through shrimp consumption could be eliminated. Even so, the chemical speciation of As in shrimp species needed further investigation. Moreover, in eutrophic lakes, the potential health risk of hepatotoxic microcystins (MCs) should be raised attention in consideration to their potential liver damage in fish and humans (Jiang et al., 2017; Jing et al., 2021). Therefore, contents of MCs in aquatic species from previous study (Jiang et al., 2017) were obtained to investigate the non-carcinogenic effect as to achieve the recommended daily intake of DHA + EPA. It was of note that the non-carcinogenic effects of MCs deserved attention because the BRQNC values for MCs was close to or higher than one (Table 4). Management strategies should be taken to control the eutrophication in the lake to reduce the MCs accumulation in fish (Jing et al., 2021).
Table 4
Results of integrated benefit-risk assessment for consumption of fish and shrimp species from Chaohu Lake, China.
Species | BRQNC | BRQC |
As | Cd | Hg | Ni | Pb | MCs | As |
HyM | 0.16 | 0.11 | 0.14 | 1.55 | 0.23 | 2.11 | 0.14 |
ArN | 0.19 | 0.10 | 0.24 | 1.86 | 0.24 | | 0.17 |
CyC | 0.10 | 0.16 | 0.81 | 1.82 | 0.34 | | 0.09 |
CaA | 0.21 | 0.18 | 0.79 | 1.46 | 0.39 | 1.82 | 0.19 |
MeA | 0.14 | 0.15 | 0.27 | 1.38 | 0.23 | 1.56 | 0.13 |
CuA | 0.12 | 0.10 | 0.30 | 0.89 | 0.16 | | 0.11 |
HeM | 0.12 | 0.23 | 0.32 | 1.84 | 0.29 | | 0.11 |
NeT | 0.28 | 0.36 | 0.37 | 1.86 | 0.41 | | 0.25 |
CoE | 0.30 | 0.16 | 0.21 | 1.10 | 0.28 | 0.94 | 0.27 |
PaM | 0.64 | 0.12 | 0.06 | 0.74 | 0.13 | | 0.58 |
MaN | 1.24 | 0.18 | 0.06 | 0.58 | 0.15 | | 1.11 |
3.5. Uncertainty of the benefit-risk assessment
In this study, benefit-risk assessment was conducted on basis of the recommended daily intake of essential fatty acids (DHA + EPA) and trace elements (Fe, I, Zn, Se, Cu, Mo, Cr), reference dose of non-essential trace elements (As, Cd, Hg, Ni, Pb), tolerable daily intake of microcystins, and cancer slope factor of As. There were uncertainties related to the benefit-risk assessment:
(1) The assessment assumed that inland residents obtained nutrients and contaminants through freshwater fish consumption, i.e. provided a fraction of food consumption, whereas excluding other dietary sources of nutrients and contaminants. Moreover, the assessment presumed that only one fish or shrimp specie was consumed in diet, yet the benefit and risk would be moderated by consumption of different species (Geng et al., 2015).
(2) For large-sized individuals, only dorsal muscles were investigated, however muscles from other portions (ventral, tail, etc) with different nutrients and contaminants were not included (Cui et al., 2018; Zhang et al., 2012b).
(3) Total content of trace elements were reported and evaluated, however, not all forms of trace elements were toxic to wildlife or humans (Lescord et al., 2020). For instance, arsenobetain and arsencholine were predominant organic-As compounds in freshwater fish (Gladyshev et al., 2020; Sobolev et al., 2019). And for Cr, the trivalent Cr was nutritionally beneficial while the hexavalent Cr was highly toxic and carcinogenic. Fortunately, Cr commonly existed in the trivalent state in natural foods (Lescord et al., 2020). Besides, cooking process might whether or not decrease the contaminant content in food. The bio-accessibility/bio-availability of nutrients and contaminants were not taken into account. Therefore, it was noteworthy that the risk of these elements to fish consumers might be over/under estimated.
(4) Besides non-essential trace elements, fish and shrimp were likely to accumulate other environmental contaminants that needed to be considered (Nostbakken et al., 2021). However, duo to the lack of corresponding RfD and CSF values, these contaminants were not included in present assessment.
(5) The average daily consumption of aquatic products for residents from the whole country, villages, cities and big cities were 29.6 g, 23.7 g, 44.9 g and 62.3 g, respectively (Zhai and Yang, 2006). Besides, it was regarded that a low fish intake of 15–35 g/d could have beneficial effect on heart disease and stroke (Du et al., 2012). However, the amount of fish consuming to fulfill the daily intake of essential fatty acids was 134.9- 355.1 g/d, which was much higher than the statistical consuming amount, thus the practical ingestion of nutrients and contaminants might be much lower for inland residents through freshwater fish and shrimp consumption (Qin et al., 2020). Nevertheless, such integrated benefit-risk assessment was necessary to provide consumers with sufficient information for healthy food choice (Gladyshev et al., 2009).