Anastario et al. 2025 — Metal profiling of Hass avocados: ICP-MS and pXRF
This pilot study quantified 24 elements across 24 Hass avocado samples using ICP-MS (primary) and portable XRF (pXRF, screening tool validation), stratifying by country of origin (California, USA vs. Michoacán, Mexico) and agricultural practice (organic vs. conventional). It provides baseline data on elemental distribution between the edible mesocarp (pulp) and exocarp (peel), finding that metals generally accumulate more in the exocarp. Notably, mercury was elevated in avocado tissues relative to comparable tropical fruits, particularly in exocarp and in USA-sourced samples, which the authors attribute to possible Hg accumulation in lipophilic matrices. Cd, Pb, and As were detected at relatively low concentrations in mesocarp.
Key numbers
Concentrations reported as geometric mean (µg/g dry weight) from ICP-MS:
Mesocarp (pulp, the edible fraction):
- K: GM ~18,000–39,000 µg/g (range across groups); notably higher in exocarp
- Mg, Ca: high macro-mineral concentrations, higher in exocarp
- Hg: detected above LOD in mesocarp; maximum mesocarp Hg approximately 0.012–0.021 mg/kg fresh weight after moisture-content adjustment — exceeds some stringent produce reference values of 0.01 mg/kg but well below seafood MRL of 0.5–1.0 mg/kg
- Co and Ni: strongest co-occurrence signature in mesocarp; elevated specifically in organic USA avocados (linked to ultramafic/volcanic soils in California)
- Pb, Cd, As: detected at “relatively low concentrations” in mesocarp (precise geometric means not fully resolvable from text extraction; detailed values in Table 1 of the original)
Exocarp (peel):
- Elemental concentrations generally higher than mesocarp for all measured metals
- Hg: geometric mean consistently higher in exocarp than mesocarp; strong co-occurrence with Mg, Fe, and Mo in exocarp
- Pb: exocarp concentrations higher than mesocarp
Organic vs. conventional differences:
- Co–Ni signature (mesocarp) present only in organic USA avocados; linked to ultramafic soil geology
- Hg more frequently elevated in USA-sourced avocados than Mexican-sourced
pXRF calibration: Strong linear correlations with ICP-MS for K, Ca, Fe, and Zn; less amenable for trace elements with frequent non-detects.
LOD: Elements reported only when consistently detected above LOD across samples; As, Cd, Pb had frequent detects at low concentrations.
Sample size note: n=24 is small (6 per origin × practice stratum); this is an explicitly pilot study and findings should not be taken as representative of the full commercial market. Authors describe this as a precursor to a larger ongoing biosocial study.
Methods (brief)
Cross-sectional pilot. ICP-MS: microwave-assisted acid digestion (trace-metal-grade HNO3), MARS 6 system. Exocarp dehydrated 57.2°C × 48 h; mesocarp × 96 h. NIST 1515 Apple Leaves used as CRM. Concentrations reported in µg/g dry weight. pXRF: Thermo Niton XL5 Plus in Soils Mode. 24 elements assessed. No arsenic speciation performed (total As reported).
Implications
Certification: Mercury findings in avocado mesocarp — though below seafood MRLs — exceed some strict produce reference values at the high end, supporting inclusion of tHg in risk monitoring for avocado-containing products. Avocado is a growing ingredient in functional foods and infant-targeting products; the Hg finding and the origin-linked Co/Ni signal are actionable for supply-chain screening guidance.
Courses: The organic/conventional difference for Ni and Co (linked to soil geology, not farming practice) is a strong illustration of why origin matters more than label for certain metals. The pXRF vs. ICP-MS calibration data are relevant to field-screening curriculum in testing methods.
App: Pilot data only; insufficient n for robust app-facing concentration distributions. Flag as provisional until a larger study is available. Matrix split (mesocarp vs. exocarp) is relevant: consumers do not eat the exocarp, so mesocarp values are the appropriate basis for dietary exposure.