Comparative exposure and risk assessment of heavy metals, nutrients, and organochlorine pesticides in cow and plant-based milks

Overview

Good and colleagues at Texas Southern University measured four heavy metals (Cr, total arsenic (As), cadmium (Cd), Pb), four macronutrients (Na, Mg, K, Ca), four micronutrients (Fe, Cu, Zn, Mn), and 24 organochlorine pesticides (OCPs) in 22 commercially available milk products purchased from Houston, Texas grocery retailers — cow milk plus seven plant-based milk alternative (PBMA) categories (almond, soy, oat, coconut, hemp, rice, cashew). Heavy metals and minerals were quantified by inductively coupled plasma mass spectrometry (ICP-MS); OCPs by gas chromatography with electron capture detection (GC-ECD) following USEPA Method 8081B. PBMAs exhibited higher and more variable concentrations of chromium (Cr), As, and Cd than cow milk, with rice milk showing the highest arsenic (0.64 µg/L) and hemp milk the highest chromium (0.68 µg/L). Lead concentrations were comparable across all milk types (0.18 to 0.28 µg/L). All measured concentrations of heavy metals fell well below applicable regulatory thresholds for drinking water and milk; the authors flag that no harmonized heavy-metal maximum limits currently apply to plant-based milk alternatives. Detectable residues of multiple OCPs (dicofol, hexachlorobenzene, mirex, toxaphene, kepone, and others) were observed across all milk categories.

Key numbers

All concentrations are reported in micrograms per liter (µg/L) of the beverage as analyzed and as consumed, per the source’s Materials and Methods (microwave-assisted acid digestion of 4 mL well-homogenized liquid milk, diluted to a final 2% HNO3 concentration, then ICP-MS quantification). Heavy metal values in Tables 1, 3, and 4 are reported as mean ± standard deviation across brands per milk type (n = 2 to 4 brands per type), with each brand analyzed in triplicate; brand-level means were treated as independent observations for the milk-type summary statistics. The arsenic figures below are total arsenic (no inorganic-arsenic speciation was performed by the authors), even though the Discussion text contextualizes potential intake against the WHO inorganic arsenic provisional tolerable daily intake.

Heavy metal concentrations by milk type (Table 1, source p. 3)

Per-analyte ranges across the eight milk categories: Cr 0.11 to 0.68 µg/L (lowest cow, highest hemp); total As 0.02 to 0.64 µg/L (lowest cow, highest rice); Cd 0.03 to 0.17 µg/L (lowest cow/cashew, highest soy); lead (Pb) 0.18 to 0.28 µg/L (lowest almond/cashew, highest coconut/soy). The authors highlight three patterns: Cr, As, and Cd were predominantly higher in PBMAs than in cow milk; rice and hemp milks led the As column; Pb concentrations were comparable across cow milk and PBMAs.

Macronutrient concentrations by milk type (Table 2, source p. 3)

Micronutrient concentrations by milk type (Table 3, source p. 4)

Organochlorine pesticide concentrations by milk type (Table 4, source p. 5; selected high-load compounds, all values µg/L)

The full Table 4 reports 24 OCPs; the six rows above are the highest-load compounds. The remaining 18 OCPs (α-Chlordane, γ-Chlordane, 4,4-DDD, 4,4-DDE, α-BHC, β-BHC, γ-BHC, Aldrin, Dieldrin, Endosulfan I/II/sulfate, Endrin, Endrin aldehyde, Endrin ketone, Heptachlor, Heptachlor epoxide, Methoxychlor) are reported in source Table 4 at µg/L concentrations ranging from approximately 1.5 (α-BHC in coconut) to ~81 (Methoxychlor in cow, almond, soy, oat, cashew). The authors group Σ24-OCP burden as approximately 6,000 µg/L for cow, almond, soy, oat, and cashew milks; approximately 3,600 µg/L for rice milk; and approximately 630 µg/L for coconut and hemp milks (Figure 4, source p. 8).

Exposure framing supplied by the authors (Discussion, source p. 5)

For a conservative daily intake assumption of 250 mL milk per day, the authors state that:

• At the upper observed range of As, Cd, and Cr in PBMAs, a single 250 mL serving would contribute a non-trivial fraction of the WHO inorganic arsenic provisional tolerable daily intake of 2.1 µg/kg body weight per day, and Cd contributions from a single serving “approach levels of concern for populations with high dietary intake.”
• For 250 mL servings of cow, almond, soy, and oat milks, the estimated Σ24-OCP daily intake is approximately 750 to 770 µg of total OCPs, compared with approximately 80 µg for coconut and hemp milks.

The authors do not compute formal hazard quotients or margin-of-exposure values for individual analytes and do not report body-weight assumptions for the consumer profile beyond the WHO PTDI reference.

Methods (brief)

Sample preparation followed microwave-assisted acid digestion. For each sample, 4 mL of well-homogenized milk was transferred into a Teflon digestion vessel with 10 mL of 70% nitric acid (HNO3); digestion conditions were 200 °C and 800 psi for 15 minutes. Digestates were diluted to a final 2% HNO3 concentration with ultrapure deionized water. Heavy metals (Cr, As, Pb, Cd) and macro/micronutrient minerals (Ca, Mg, Na, K, Fe, Cu, Zn, Mn) were quantified on an Agilent 7900 ICP-MS with calibration standards of 0.05 to 100 µg/L prepared from multi-element stock solutions; helium collision gas mode was used to minimize polyatomic interferences; internal standards (scandium, yttrium, terbium) corrected for matrix effects and instrumental drift. The Methods text notes “need to add reference #31 here” in a sentence regarding the ICP-MS conditions, an editorial placeholder that does not affect the reported data.

OCP extraction followed USEPA Method 8081B with liquid-liquid extraction in a 1:1 hexane-acetone mixture and silica gel cleanup to remove lipids. OCP quantification used an Agilent 6890 GC-ECD with dual Restek Rtx-CL Pesticides columns, nitrogen carrier gas at 4.3 mL/min, injector at 250 °C, ECD at 340 °C, oven program 120 °C (3-min hold) ramped to 310 °C (1-min hold). Calibration used EPA 500-series OCP standards spanning 0.5 to 500 µg/kg.

Sample handling: products were purchased in their original retail containers (HDPE bottles, aseptic cartons, glass bottles); container material was recorded and the authors report no statistically meaningful differences associated with packaging. Samples were transported under temperature-controlled conditions, stored at 4 °C in the dark, and analyzed within 72 hours of purchase. Quality control: triplicate injections of each sample; matrix spike samples fortified with known analyte concentrations; recoveries of 80 to 120% accepted per AOAC method-validation guidelines (AOAC Appendix F). No speciation was performed for arsenic, mercury, or chromium; reported values are total Cr, total As, total Cd, and total Pb.

Statistical analysis: all concentrations reported as mean ± standard deviation across brands per milk type. Each commercial brand was analyzed in triplicate; arithmetic mean of triplicate measurements represents each brand; brand-level means treated as independent observations for milk-type summary statistics. The standard deviation reflects between-brand variability rather than analytical precision. Per-category brand replication (n) is small (n = 2 to 4 per milk type), and no formal hypothesis testing was performed. The authors describe the study as exploratory.

Limitations explicitly named by the authors: small sample set with limited brand replication per category (not capturing full commercial variability); samples purchased in Houston but products originated from broader national or international supply chains (findings not specific to any production region); cross-sectional design (no seasonal or batch-to-batch variation captured); no chemical speciation, bioaccessibility, or cumulative dietary exposure assessment.

Related evidence

• Plant milk base
• Almond
• Coconut
• Oat
• Soy Milk
• Soy
• Rice Milk
• Rice
• Cashews
• Non Rice Grains
• Milk and Dairy
• Plant Milks (Almond, Oat, Coconut, Other Non-Soy/Non-Rice)
• Plant Milks, Rice-Based — RETIRED
• Plant Milks, Soy-Based
• Rice beverages (rice milk)
• Chromium
• Arsenic, Total
• Cadmium
• Lead

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