Enhanced levels of hazardous trace elements (Cd, Cu, Pb, Se, Zn) in bird tissues in the context of environmental pollution by Raša coal

Overview

This study measured 13 elements (Al, V, Cr, Mn, Fe, Co, Cu, Zn, As, Se, Mo, Cd, Pb) by ICP-MS in muscle, liver, kidney, and brain of 12 wild birds (pigeon, jay, mallard, magpie) from the Raša coal-polluted area of eastern Istria, Croatia and 8 control-area birds (pigeon, pheasant, jay) from the Kontija Forest ~35 km west of the pollution source. Of the 13 elements, the authors report distributions for 5 (Se, Cd, Pb, Cu, Zn) selected for elevated occurrence in the polluted environment. Mean Se and Cd were significantly elevated in Raša-area birds vs control (Se muscle p=0.003, Se liver p=0.04, Cd kidney p=0.01 by Mann–Whitney U). Highest Cu, Zn, and Se concentrations occurred in liver; highest Cd and Pb in kidney. Mallard kidney Cd (mean 2.30 mg/kg w.w.) and pigeon kidney Cd (1.43 mg/kg w.w.) exceed the Croatian Ordinance 146/12 maximum allowable Cd in poultry kidney (1.0 mg/kg w.w.) used as a reference standard because no game-bird-specific Croatian Cd threshold exists. The authors nonetheless conclude human-health risk from consumption of these game species is very low because mean annual game-meat consumption in Croatia is only 0.3 kg per household member (Croatian Statistical Yearbook 2011).

Key numbers

Table 1 — Pooled-species Raša (R, n=12) vs Control (C, n=8) descriptive statistics by tissue (mg/kg w.w.; brain C n=6 for all metals, brain R n=11 and brain C n=6 for Pb specifically, kidney C n=7 for Pb specifically):

(Internal-mirroring caveat in source Table 1: the “Cu liver R” row gives mean 17.7, Q1 3.32, Q3 234 — the Q3 of 234 mg/kg w.w. is clearly mislabelled in the source given that the column max is 68.1 and the Q1 is 3.32; the published value is reproduced verbatim. See Verification notes.)

Table 2 — Per-species mean concentrations in Raša-area pigeon, mallard, and magpie (mg/kg w.w.):

(Jay per-species means are reported in Table 3 of the source, not Table 2.)

Table 4 — Mann–Whitney U test p-values, Raša vs control area, all-bird pooled (bold = significant at p < 0.05):

Table 5 — Croatian Ordinance 146/12 maximum permitted concentrations applied as reference standards (no game-bird-specific values exist; poultry values used by the authors as the closest applicable reference):

Authors’ fitness-for-consumption comparison (page 27–28):

• Mallard liver Cd mean (0.756 mg/kg w.w.) exceeds the Ordinance 146/12 poultry-liver Cd limit of 0.5 mg/kg w.w.
• Pigeon kidney Cd mean (1.43 mg/kg w.w.) and mallard kidney Cd mean (2.30 mg/kg w.w.) exceed the Ordinance 146/12 poultry-kidney Cd limit of 1.0 mg/kg w.w.
• All-bird-pooled mean Pb in Raša-area muscle (0.0364), liver (0.232), kidney (0.249), and brain (0.0138 mg/kg w.w.) are below the Croatian reference thresholds and below the Franson & Pain (2011) 2 mg/kg w.w. liver/kidney bird-poisoning threshold and the Kalisinka (2000) 1.5 mg/kg w.w. brain Pb poisoning threshold.
• Authors’ conclusion: human-health risk from consumption of meat and offal of these species in the study area is “very low,” because average annual game-meat consumption in Croatia is 0.3 kg per household member (Croatian Statistical Yearbook 2011) and large-game species (deer, wild boar, roe deer) are consumed more than feathered game (ducks, pigeons).

Methods (brief)

Sampling: 20 wild birds collected December 2019 – January 2020 in eastern Istria, Croatia. Raša coal-polluted area (n=12): 5 wild pigeons and 2 mallards from the mouth of the Raša River, 1 pigeon from Koromačno, 1 mallard from Polje Čepić, 1 magpie from Brgod, and 2 jays from Gora Glušići. Control area (n=8): Kontija Forest above the Lim Channel on the west coast of Istria (~35 km west of the pollution source), 6 wild pigeons plus pheasants and jays.

Sample prep: 0.5 g homogenised tissue was weighed into a Teflon liner with 3 mL H₂O + 2.5 mL HNO₃ (65%). High-pressure microwave digestion (Multiwave 3000, Anton Paar, Graz, Austria) in three steps: (I) 5 min at 500 W, (II) 20 min at 1000 W, (III) 30 min at 1200 W. Cooled, transferred to a 50 mL volumetric flask, filled to mark with ultra-pure water. Internal-standard mixture (In, Bi, Sc; Inorganic Ventures, Blacksburg, VA, USA) added on-line via the standard ISTD mixing tee.

Instrumentation: Agilent ICP-MS Model 7900 (Agilent, Palo Alto, CA, USA), high-purity Ar (99.999%, White Martins, Brazil). Calibration using certified Environmental Calibration Standards at 99.999% purity for Se, Cd, Pb, Cu, Zn at 10 mg/L (Agilent Technologies, USA).

Statistical analysis: Descriptive statistics (mean, median, min, max, Q1, Q3, SD) by tissue × area. Mann–Whitney U test for Raša vs control area comparisons; significance level p < 0.05.

Speciation: total arsenic and total mercury are not separately reported in the paper’s results; the 5 elements selected for detailed reporting (Se, Cd, Pb, Cu, Zn) are reported as total. The metals field uses Cd, Pb, Cu, Zn, Se without speciation tags because these elements either do not require speciation (Cu, Zn) or were measured as total concentration (Cd, Pb, Se as total Se).

Basis: all values expressed in mg/kg wet weight (w.w.). Where literature comparisons in Table 2 of the source are drawn from studies reporting dry weight, the authors recalculated those values to w.w. assuming 70% water content in bird tissue (Table 2 caption).

Implications

Certification: Game-meat threshold setting is not currently a high-priority HMTc row, and no game-bird-specific maximum levels exist under Croatian or EU food law (the Croatian Ordinance 146/12 covers cattle, sheep, pigs, poultry, and horses only; the EU Regulation 1881/2006 / 2023/915 successor covers meat and edible offal of livestock without a game-bird subcategory). This paper documents that under coal-pollution context, mallard kidney and pigeon kidney Cd routinely exceed the poultry-kidney reference threshold of 1.0 mg/kg w.w. (mean 2.30 and 1.43 mg/kg w.w. respectively), and mallard liver Cd exceeds the poultry-liver reference threshold of 0.5 mg/kg w.w. (mean 0.756 mg/kg w.w.). For routing into the game-meats HMTc row, the kidney-offal Cd signal is the dominant risk pathway in this dataset.

Courses: Useful as a case study in (1) bioindicator design — birds as longest-best-studied bioindicators of environmental pollution; tissue choice (kidney/liver for long-term exposure, blood for short-term, bone for cumulative); (2) the distinction between essential trace elements (Cu, Zn, Se) showing adequate-to-high but not poisoning-range concentrations in liver and the non-essential trace elements (Cd, Pb) accumulating in kidney; (3) source attribution — Se and Cd are the elements the surrounding superhigh-organic-sulphur Raša coal characteristically enriches (Medunić et al. 2016, 2018a, 2020, 2021), and Se and Cd are the elements with significant Raša-vs-control differences in this study; (4) the species-mix effect — mallards (waterfowl, aquatic-food diet) show systematically higher Se and Cd than pigeons/jays/magpies (terrestrial diet) because Se and Cd bioaccumulate rapidly in aquatic sediments and food webs.

App: Provides Croatian wild-bird occurrence data for the game-meats product page and the meat-and-poultry / organ-meats ingredient pages. Per-species, per-tissue concentration means are reported for Cu, Zn, Se, Cd, Pb for pigeon, mallard, and magpie (Table 2 above) and Raša-vs-control descriptive statistics for the pooled-species sample (Table 1 above). Sampling year range 2019–2020 anchors this dataset toward the recent end of the wild-bird literature.

Microbiome: Not addressed.

Related evidence

• regulations/…
• Meat and Poultry
• Organ Meats (Kidney and Liver)
• Game meats (venison, bison, rabbit)
• Cadmium
• Lead
• Copper
• Zinc

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