Sacchi et al. 2021 - Balangero groundwater background metals

Sacchi and colleagues derived natural background levels for potentially toxic elements in groundwater around the former Balangero and Corio asbestos mine in serpentinite in Piedmont, North Italy. The study is primary groundwater and hydrogeochemical evidence for Cr, Cr(VI), Ni, Mn, Fe, Zn, and Co in a naturally enriched mining setting. It is not food, ingredient, consumer-product, or finished drinking-water occurrence evidence.

Key numbers

Site and regulatory context

The Balangero and Corio asbestos mine operated from the 1920s to the 1990s and was described as the largest asbestos mine in Western Europe. The area was declared an Italian Contaminated Site of National Interest in 1998. The study area includes serpentinite of the Lanzo Massif, the Sesia-Lanzo zone, fluvioglacial deposits, and the Balangero Plain aquifer.

The Italian groundwater threshold values used by the paper were:

The hydrochemical facies was mainly Mg-HCO3, tending toward Mg-SO4 with increasing mineralization. Field values across the 2019 complete characterization were circumneutral: pH 6.17-8.70, Eh 191-444 mV, and dissolved oxygen 1.90-10 mg/L.

Sampling and retained monitoring stations

A complete hydrogeochemical characterization sampled 30 monitoring stations from 25 June to 4 July 2019 after a rainy period. One station in the Balangero Plain aquifer was eliminated by the guideline pre-selection screen because nitrate exceeded the paper’s anthropogenic-indicator threshold of 37.5 mg/L. Total hydrocarbons were below the 350 ug/L limit in all samples.

For the 29 retained monitoring stations, the representative-value table reported these maximum concentrations:

The same retained-station table included below-detection counts among 29 monitoring stations:

Proposed natural background levels

The authors concluded that using a per-station median would discard high values that can be natural in this setting. They proposed using all available measurements instead, excluding two low-redox stations for the Cr, Cr(VI), Ni, and Mn calculation, and using a lower percentile for Fe and Zn.

The final source-proposed natural background levels were:

The paper states that the Cr(VI) NBL is not representative of the Balangero Plain aquifer because detectable Cr(VI) concentrations occurred in only six monitoring stations, mostly at the mountain foothills.

Methods (brief)

Wells were purged by three to four well volumes where possible. Field measurements included temperature, Eh, electrical conductivity, pH, dissolved oxygen, and alkalinity. Water samples for cations and potentially toxic elements were filtered to 0.45 um and acidified.

Potentially toxic elements were measured by ICP-OES, except Cr(VI), which was measured by UV-VIS spectrophotometry. Charge-balance errors were required to be below 10%. The reported detection limit for the potentially toxic elements was 1 ug/L, except Cr(VI), which had a 3 ug/L detection limit. Values below detection were substituted with half the detection limit for statistical treatment.

The natural-background-level workflow followed Italian guideline pre-selection, trend checks where possible, representative-value evaluation, and percentile selection by dataset confidence class. The authors classified the case as type B, meaning adequate spatial dimension but inadequate temporal dimension, and described the final NBLs as medium-confidence estimates except for Cr(VI).

Implications

Certification: Do not use this source in HMTc food, ingredient, product, or drinking-water occurrence pools. It measures groundwater at a former asbestos mine and derives natural background levels for an Italian environmental remediation setting.

App: Useful as environmental-pathway context for distinguishing geogenic/natural-background metal exceedances from anthropogenic contamination, especially for Cr(VI), Ni, Mn, Fe, and Zn in serpentinite or mine-influenced groundwater.

Courses: Useful for teaching why total Cr and Cr(VI) must remain separate, why non-detect handling affects percentile estimates, and why natural-background percentiles are not regulatory ceilings or product standards.

Wiki pages this source may touch

• chromium
• chromium-hexavalent
• cobalt
• nickel
• manganese
• iron
• zinc
• soil-to-plant-transfer
• index

Verification notes

This page was built from the full PDF, including the abstract, study-area geology, hydrogeological setting, Materials and Methods, sampling and analytical methods, Tables 1-9, the natural-background-level discussion, conclusions, supplementary-material description, and data-availability statement. Products and ingredients are intentionally empty because no food, crop, ingredient, consumer product, bottled water, or finished drinking-water sample was analyzed. Cr(VI) is kept separate from total Cr. The proposed NBL values are the paper’s environmental background estimates and are not HMTc standards or pooled benchmark percentiles.

Page history

The five most recent substantive edits to this page. The full version history lives in git; when DOI minting comes online (see schema docs), each entry below will also link to a version-pinned DataCite DOI.