Gómez-Arroyo et al. 2017 — Dandelion as heavy metal biomonitor, Mexico City metropolitan area
Gómez-Arroyo and colleagues used leaves of Taraxacum officinale (common dandelion) as a passive biomonitor to assess atmospheric heavy metal deposition across two contrasting zones of the Mexico City Metropolitan Area (MAMC): an urban campus site (Centro de Ciencias de la Atmósfera, CCA-UNAM) and a peri-urban high-altitude station (Altzomoni, Iztaccíhuatl-Popocatépetl National Park). In addition to measuring metal concentrations by atomic absorption spectrophotometry, the authors quantified expression of microRNA-398 (miR398) and its target gene superoxide dismutase 2 (CSD2) as molecular stress indicators, and used the MTT reduction assay to estimate oxidative stress (free radical production). The combination of chemical measurement and plant stress physiology is the paper’s methodological novelty.
Key findings
Metal concentrations in dandelion leaves were consistently higher in the dry season than the rainy season at both stations, consistent with greater atmospheric deposition during Mexico City’s dry season and reduced wet deposition during rains. The Altzomoni station showed particularly elevated concentrations of five metals — most notably aluminum, cadmium, chromium, nickel, and lead — in the dry season, which the authors attribute partly to volcanic dust from the nearby Popocatépetl volcano. The CCA-UNAM urban site showed high vanadium and cadmium concentrations, consistent with petroleum combustion emissions from traffic and industry in the urban core.
Metal concentrations are reported in µg/g dry weight in the leaves but the paper presents them primarily as figures (bar charts with error bars) rather than tabulated values; exact means are readable from Figure 1. Lead was detected at high concentrations in both seasons at both stations, with CCA showing higher Pb in the rainy season (contrary to the dry-season dominance seen for most metals), which the authors attribute to atmospheric re-suspension of street dust. The molecular markers (miR398, CSD2, MTT) followed metal concentration patterns: dry-season samples with higher metal loads showed higher CSD2 expression and higher reduced MTT (oxidative stress indicator), supporting the interpretation that the measured concentrations were biologically significant.
Methodological notes
Metal concentrations in plant tissues were measured by atomic absorption spectrophotometry (GBC AVANTA g). The paper states that standards were within the expected concentration range from traceable reference standards and that the detection limit was defined as three times the standard deviation of the background noise. No LOD/LOQ values are tabulated; this limits the paper’s utility for quantitative occurrence synthesis but does not undermine its biomonitoring conclusions.
The dandelion was selected as biomonitor because it is a cosmopolitan species, grows in varied urban and peri-urban environments, is easy to identify and collect, and has documented capacity to accumulate metals from both soil and atmospheric sources via leaf surface adsorption. The authors note that lead, in particular, is likely partly absorbed into the cuticle from atmospheric deposition rather than fully translocated from soil roots, a distinction relevant to interpreting dandelion leaf Pb concentrations as predominantly atmospheric rather than soil signals.
Relevance to this wiki
This paper is not a food occurrence study. Dandelion leaves consumed as food (which is a practice in parts of Europe and Mexico) would be one application of the data, but the paper does not frame it that way. The primary relevance to this wiki is threefold. First, it provides atmospheric-deposition context for the supply-chain section: urban and peri-urban growing areas in highly polluted MAMC can expose leafy crops to metal loads from atmospheric sources independently of soil metal status. Second, the dry-season/rainy-season variation data support the seasonal variance framing on ingredient pages for leafy vegetables grown in urban Mexico. Third, the molecular stress-response data (miR398/CSD2) illustrate the plant-side mechanisms that accompany metal accumulation and that mediate nutritional quality degradation consistent with Khan et al. 2015.
Implications
Supply chain: supports soil and any future atmospheric-deposition page with evidence that atmospheric deposition can be a significant, geography-specific metal source for leafy crops — not just soil.
Ingredients: marginal relevance to leafy-vegetables for the urban-Mexico geographic context.
Microbiome: none.