# Metal Bioaccumulation by Carp and Catfish Cultured in Lake Chapala, and Weekly Intake Assessment
## 4 Discussion
Another factor that plays a role in the uptake of metals in aquatic organisms is pH. Lake Chapala maintained a pH of 8.6-9.5 during our experiment [6]. This alkaline pH promotes the aggregation of metals into particles that settle, thus reducing their dissolution in the liquid phase [5]. This explains the low metal concentration found in the water of Lake Chapala despite the high concentration of its sediments [6]. The data in Table 5 indicate the EWI levels for the fish from Lake Chapala in the experimental and control groups, and all of them were below 1% of the PTWI. Regarding the intake of Cu and Zn by fish consumption as essential metals, the values obtained are part of normal human dietary requirements. The risk of consuming fish revolves around their content of non-essential heavy metals. Table 6 presents the comparison of the EWI and % PTWI estimated during the present study from the fish cultivated in Lake Chapala, with other reports of cultured and wild freshwater fish. Table 6 shows that the EWI and % PTWI values for Cd in the present work were similar (0.11%), although lower than the unique report of cultured carp (0.35%) [30], as well as others reports of wild fish from lakes [30; 37]. On the other hand, some previous works showed EWI up to two orders of magnitude higher than our work (0.395 and 0.743), and PTWI higher than 5%, which is indicative of caution [12; 38]. The EWI values for lead in the present work were one or two orders of magnitude lower than previous reports, as shown in Table 5. [PERSON] et al. [12] showed the highest EWI values for lead in native catfish (7.307 \(\mathrm{\SIUnitSymbolMicro g}\)/kg of bw) living in a dam environment. According to the authors, the causes were a natural, local source of Pb, runoff from rain, and residue from extractive mining. It is interesting to notice that [PERSON] et al. [12] and [PERSON] and [PERSON] [38] reported the highest % PTWI in two metals, Cd and Pb. The EWI for As obtained in the present work for carp (0.163 \(\mathrm{\SIUnitSymbolMicro g}\)/kg of bw) was lower, although it resulted in the same range as those reported by [PERSON] et al. [30] for native and cultured carp (0.271 and 0.511 \(\mathrm{\SIUnitSymbolMicro g}\)/kg of bw, respectively). The water concentrations during experiments were slightly higher in Lake Chapala (9.22-11.0 \(\mathrm{\SIUnitSymbolMicro g}\)/L) [6] compared to the values reported by [PERSON] et al. [39] (0.72 to 3.1 \(\mathrm{\SIUnitSymbolMicro g}\)/L). Regarding EWI for catfish, the obtained 0.093 \(\mathrm{\SIUnitSymbolMicro g}\)/kg of bw agrees with [PERSON] et al. [9], who reported 0.189 \(\mathrm{\SIUnitSymbolMicro g}\)/kg of bw in the same type of fish. The As water concentration reported by [PERSON] et al. [9] (1.34-5.65 \(\mathrm{\SIUnitSymbolMicro g}\)/L) was in a similar range as that in the present study. The % PTWI was less than 5% in the previous reports and agrees with their water and fish As concentration. Mercury is the principal toxic metal of concern in terms of consuming fish and seafood, which constitute the primary sources of this metal [40]. In the present study, Hg had 0.61% and 4.9% of the PTWI in carp and catfish, respectively. Based on the mean mercury concentrations reported by [PERSON] et al. [41], [PERSON] et al. [10], and [PERSON] et al. [11] for native carp from Lake Chapala, a decrease in the concentration is noted over time that results in a lower weekly intake from native fish that represented a contribution to the PTWI of 155.36% in 2010 and 40.89% in 2014. Clearly, these figures are much higher than the results of our study, emphasizing the decrease in metal accumulation that is evident in fish cultured in floating cages. In another study, [PERSON] et al. [12] reported an EWI of a dam catfish (0.124 \(\mathrm{\SIUnitSymbolMicro g}\)/kg of bw), while [PERSON] and [PERSON] [42] reported a figure of 0.467 \(\mathrm{\SIUnitSymbolMicro g}\)/kg of bw for native lake roach from the family _Cyprinidae_, representing contributions to the PTWI of 9.49% and 26%, respectively.