Rodriguez-Mendivil et al. 2019 — Heavy metals in canned tuna and fresh fish, Tijuana, Mexico
This 2019 peer-reviewed study measured total Hg (tHg), Pb, Cd, and Cr in 48 canned tuna samples from 8 brands and 20 fresh fish samples from 4 species sold in Tijuana, Mexico, then calculated hazard quotients (HQs) and total hazard quotients (THQs) using the USEPA region III risk-based concentration table. Note that mercury was measured as total Hg by cold vapor atomic absorption spectrometry (CVAAS) — the paper does not speciate MeHg from inorganic Hg. All HQ and THQ values fell below 1.0, indicating no significant health risk at prevailing consumption rates for the Mexican general population; however, two canned tuna samples (4.16%) exceeded Mexico’s 1.0 mg/kg maximum permissible limit for Hg, and two samples exceeded the EU Pb limit of 0.20 mg/kg.
Key numbers
Canned tuna (n=48, wet weight, mg/kg)
| Brand | Hg range | Hg mean ± SD | Pb range | Pb mean ± SD | Cd range | Cd mean ± SD | Cr range | Cr mean ± SD |
|---|---|---|---|---|---|---|---|---|
| M1 (n=6) | 0.150–0.650 | 0.304 ± 0.199 | 0.070–0.110 | 0.091 ± 0.016 | 0.000–0.004 | 0.0019 ± 0.0014 | 0.020–0.210 | 0.123 ± 0.068 |
| M2 (n=6) | 0.130–0.540 | 0.292 ± 0.153 | 0.090–0.130 | 0.109 ± 0.015 | 0.0004–0.005 | 0.0027 ± 0.0018 | 0.020–0.045 | 0.170 ± 0.163 |
| M3 (n=6) | 0.110–0.670 | 0.366 ± 0.216 | 0.090–0.130 | 0.113 ± 0.014 | 0.0003–0.005 | 0.0029 ± 0.0021 | 0.070–0.300 | 0.191 ± 0.102 |
| M4 (n=6) | 0.110–1.170 | 0.560 ± 0.450 | 0.080–0.320 | 0.174 ± 0.105 | 0.0009–0.006 | 0.0034 ± 0.0017 | 0.080–0.650 | 0.270 ± 0.199 |
| M5 (n=6) | 0.230–0.840 | 0.405 ± 0.243 | 0.110–0.130 | 0.120 ± 0.007 | 0.0026–0.007 | 0.0040 ± 0.0015 | 0.120–0.260 | 0.166 ± 0.049 |
| M6 (n=6) | 0.005–0.320 | 0.116 ± 0.115 | 0.090–0.120 | 0.104 ± 0.009 | 0.0008–0.006 | 0.0032 ± 0.0023 | 0.060–0.180 | 0.123 ± 0.045 |
| M7 (n=6) | 0.030–0.210 | 0.115 ± 0.070 | 0.080–0.100 | 0.086 ± 0.008 | 0.0003–0.007 | 0.0031 ± 0.0029 | 0.050–0.400 | 0.182 ± 0.136 |
| M8 (n=6) | 0.060–0.280 | 0.140 ± 0.094 | 0.080–0.140 | 0.103 ± 0.020 | 0.0006–0.003 | 0.0020 ± 0.0010 | 0.080–0.170 | 0.113 ± 0.032 |
Overall canned tuna (n=48, combined): Hg 0.005–1.170, mean 0.278; Pb 0.07–0.32, mean 0.113; Cd 0.000–0.007, mean 0.0029; Cr 0.02–0.65, mean 0.167 mg/kg ww.
Fresh fish (n=20, wet weight, mg/kg)
| Species | n | Hg range | Hg mean ± SD | Pb range | Pb mean ± SD | Cd range | Cd mean ± SD | Cr range | Cr mean ± SD |
|---|---|---|---|---|---|---|---|---|---|
| Mako shark (I. oxyrinchus) | 5 | 0.690–2.140 | 1.286 ± 0.601 | 0.100–0.320 | 0.159 ± 0.093 | 0.001–0.003 | 0.0023 ± 0.0005 | 0.160–0.380 | 0.216 ± 0.093 |
| Soupfin shark (G. galeus) | 5 | 0.460–1.810 | 1.128 ± 0.522 | 0.040–0.130 | 0.096 ± 0.032 | 0.001–0.002 | 0.0018 ± 0.0002 | 0.070–0.180 | 0.137 ± 0.042 |
| Swordfish (X. gladius) | 5 | 0.380–0.720 | 0.545 ± 0.123 | 0.080–0.160 | 0.119 ± 0.030 | 0.001–0.003 | 0.0022 ± 0.0004 | 0.150–0.180 | 0.168 ± 0.014 |
| Yellowfin tuna (T. albacares) | 5 | 0.140–0.570 | 0.377 ± 0.161 | 0.090–0.150 | 0.116 ± 0.026 | 0.001–0.002 | 0.0019 ± 0.0001 | 0.080–0.130 | 0.102 ± 0.020 |
60% of fresh fish samples had Hg concentrations above the Mexican MPL of 1.0 mg/kg. Both shark species (mako mean 1.286 mg/kg, soupfin mean 1.128 mg/kg) exceeded the MPL on average.
Detection limits (mg/kg): Pb 0.01, Cd 0.001, Cr 0.01, Hg 0.000003.
Hazard quotients (THQ for canned tuna and fresh fish species, worst-case scenario: EF=365 days/yr, IR=3.4 g/day canned tuna, 3.7 g/day fresh fish, BW=70 kg, ED=75 yr):
- Canned tuna (all brands): THQ range 0.0696–0.2615, mean 0.1327 — below 1.0
- Mako shark: THQ 0.545
- Yellowfin tuna (fresh): THQ 0.156
- Soupfin shark: THQ 0.397
- Swordfish: THQ 0.209
- All values <1.0; Hg dominates the HQ for all species
Regulatory comparison:
- Mexican MPL for Hg in canned fish: 1.0 mg/kg; 2/48 samples exceeded (1.17 and 1.04 mg/kg)
- EU regulation (EC No. 1881/2006) Pb limit: 0.20 mg/kg; 2/48 canned tuna samples exceeded (0.322 and 0.289 mg/kg)
- EU Cd limit: 0.10 mg/kg; all samples below
Methods (brief)
Total mercury measured by cold vapor atomic absorption spectrometry (CVAAS), USEPA method 7471b, after microwave-assisted acid digestion. Pb, Cd, and Cr measured by graphite furnace atomic absorption spectroscopy (GFAAS), USEPA method 7010, after microwave-assisted digestion. Quality control: certified reference materials ERA 524 (Pb, Cd, Cr) and ERA 027 (Hg); recoveries 95–105% for QC standards, 85–102% for spikes. Note: mercury is measured as total Hg; no speciation between MeHg and inorganic Hg is performed. Consumption rate assumptions for hazard quotient calculation are derived from national per capita consumption data for Mexico (1.23 kg/yr canned tuna, 1.34 kg/yr fresh tuna equivalent), representing a worst-case scenario treating all fish species as if consumed at the fresh tuna rate.
Implications
Certification: The tHg data for canned tuna (mean 0.278 mg/kg, max 1.170 mg/kg ww) and yellowfin tuna fresh (mean 0.377 mg/kg) are measured as total Hg, not MeHg — relevant context when comparing against HMT&C MeHg thresholds. The Cr concentrations (canned tuna mean 0.167 mg/kg, up to 0.65 mg/kg) are substantially higher than reported in other studies; the authors note no MPL exists for Cr in Mexican or EU regulations for these matrices, but the values are worth flagging in any Cr monitoring context. Cd is very low across all samples.
Courses: Illustrates the species-dependent tHg gradient from canned yellowfin tuna (mean 0.278 mg/kg) through fresh yellowfin tuna (0.377 mg/kg) to shark species (mako 1.286 mg/kg) — useful for teaching biomagnification and species-selection as a contamination lever.
App: Provides canned tuna tHg range (0.005–1.170 mg/kg) and Pb range (0.07–0.32 mg/kg) with brand-level variance data from Mexico; the Cd data (max 0.007 mg/kg) confirms very low Cd burden in canned tuna across this dataset.