BACKGROUND
This study examined spatial and temporal variability in trace and macro elements in the red crab, *Pleuroncodes planipes*, collected off the Pacific coast of the Baja California Peninsula, Mexico. The rationale was that element content in seafood can vary with environmental conditions, including El Niño, upwelling, depth distribution, and diet, and that this matters for both ecology and food safety. The authors focused on calcium (Ca), cadmium (Cd), copper (Cu), iron (Fe), lead (Pb), magnesium (Mg), manganese (Mn), nickel (Ni), phosphorus (P), and zinc (Zn). The red crab is an abundant decapod crustacean used primarily to produce flour for aquaculture feed, but it has also been considered a possible ingredient for human nutrition. Because some elements are essential at low levels but harmful at high levels, the authors assessed both environmental variability and potential human health risk.
METHODS
The study area extended from latitude 23°19′ N–longitude 110°45′ W to latitude 28°51′ N–longitude 114°42′ W along the west coast of the Baja California Peninsula. Three research cruises were analyzed: C1 from 21 October to 10 November 2004, C2 from 15 March to 29 March 2005, and C3 from 21 November to 4 December 2006. C1 and C3 occurred during El Niño conditions, while C2 was during a neutral year, based on a threshold of ±0.5 °C in the Oceanic Niño Index. The authors analyzed 279 whole adult crabs ranging between 32 mm and 40 mm. Samples were dried for 72 h at 70 °C and digested with concentrated HNO3 and 30% H2O2. Element concentrations were measured by atomic absorption spectrophotometry, while phosphorus was measured by the molybdovanadate method. Recovery values ranged from 93% to 116%. Detection and quantification limits (µg g−1) were, respectively, Ca: 0.08 and 0.10; Cd: 0.01 and 0.02; Cu: 0.01 and 0.02; Fe: 0.65 and 1.35; Mg: 0.05 and 0.08; Mn: 0.04 and 0.07; Ni: 0.03 and 0.05; Pb: 0.02 and 0.07; Zn: 0.02 and 0.06. Concentrations were expressed in dry weight. Statistical analysis used two-way ANOVA with cruise and zone as fixed factors, Bonferroni post hoc testing, discriminant analysis, and factor analysis. Health risk assessment converted values to fresh weight using crab moisture of 73.8–79.4%, then estimated intake assuming 41 g day−1 consumption and 70 kg body weight.
KEY RESULTS
No detectable Pb levels were found in any sample, with all values <0.07 µg g−1. Multivariate testing showed significant differences by cruise, zone, and cruise × zone interaction, with Wilks values of 0.114642 for cruise, 0.470140 for zone, and 0.154107 for cruise × zone; all had p = 0.00. By cruise, mean Cd was 12.07 ± 0.76 in C1, 9.27 ± 0.24 in C2, and 8.97 ± 0.28 in C3. Mean Zn was 71.34 ± 3.04, 63.00 ± 0.76, and 56.88 ± 1.03, respectively. Mean Cu was 40.46 ± 4.44, 49.35 ± 1.75, and 41.21 ± 1.03. Mean Ni was 1.23 ± 0.26, 1.56 ± 0.16, and 3.19 ± 0.23. Mean Fe was 127 ± 11, 162 ± 5, and 111 ± 8. Mean Ca was 8.41 ± 0.22, 9.05 ± 0.007, and 7.27 ± 0.12 mg g−1. Mean Mg was 0.97 ± 0.03, 1.09 ± 0.02, and 1.09 ± 0.01 mg g−1. Mean P was 0.97 ± 0.04, 1.13 ± 0.02, and 0.67 ± 0.02 mg g−1. Post hoc testing showed significant differences in Cd, Zn, Cu, Fe, and Mg between C1 vs. C2; in Zn, Cu, Ni, Fe, Ca, and P between C2 vs. C3; and in Cd, Zn, Cu, Ni, Fe, Ca, Mg, and P between C1 and C3. The authors noted positive temperature anomalies of up to 0.9 °C in October–November 2004 and 1.1 °C in November 2006, while March 2005 had positive anomalies of 0.3 °C.
Spatially, the south zone had the highest Cd, Cu, Mn, and Fe values, and the north had the lowest Cd and Fe. South zone means were Cd 10.10 ± 0.32, Cu 48.78 ± 1.26, Mn 7.59 ± 0.46, Fe 155 ± 7, Ca 8.22 ± 0.13 mg g−1, Mg 1.09 ± 0.01 mg g−1, and P 0.95 ± 0.03 mg g−1. Center zone values were generally lowest, including Zn 57.32 ± 0.77, Cu 39.35 ± 1.33, Mn 4.20 ± 0.45, Fe 100 ± 6, Ca 7.32 ± 0.13 mg g−1, and Mg 1.04 ± 0.01 mg g−1. The highest Cd concentration observed was 23.10 µg g−1 in the south. Ni and P did not differ significantly among zones. Discriminant analysis showed strong separation among cruises, with Wilks’ Lambda = 0.149, F = 47.30, and p < 0.000. Root 1 explained 91% of the cumulative variance and was driven mainly by Mn, Ni, Fe, Ca, Mg, and P. Root 2 explained 9% and was driven by Cd, Zn, and Cu.
CLINICAL IMPLICATIONS
This was not a clinical trial, but its food-safety implications are relevant. Based on a 41 g day−1 intake, estimated daily intake values were low: Cd 1.33 × 10−03, Cu 6.31 × 10−03, Fe 1.90 × 10−02, Mn 7.86 × 10−04, Ni 2.96 × 10−04, Zn 9.59 × 10−03, Ca 1.23 × 10+01, Mg 1.57 × 10+00, and P 1.40 × 10+00. Percent recommended daily intake was 0.70 for Cu, 0.24 for Fe, 0.03 for Mn, 0.03 for Ni, 0.09 for Zn, 1.03 for Ca, 0.37 for Mg, and 0.20 for P. Relative to reference dose, %RfD was 1.90 × 10+00 for Cd, 2.25 × 10−01 for Cu, 3.88 × 10−02 for Fe, 8.02 × 10−03 for Mn, 2.11 × 10−02 for Ni, and 4.57 × 10−02 for Zn. The authors concluded that red crab consumption, at the modeled amount, poses no meaningful toxicological risk and contributes less than 1% of trace-element nutritional requirements and approximately 1% for Ca. Clinically, this supports red crab as a low-risk seafood from a heavy-metal exposure standpoint under the consumption assumptions used, but not as an important mineral source.