Richardson (2025) measured trace and macroelements in maple sap, finished maple syrup, and paired soils from four suburban sites in the northeastern United States, using ICP-OES for macroelements and ICP-MS for 13 trace elements. All 16 syrup batches were compared against FDA food and EPA drinking-water regulatory limits. The paper finds that finished syrup from all four sites exceeded regulatory limits for arsenic, cadmium, nickel, and zinc, and that three of four sites exceeded the limit for lead. Equipment materials are identified as a major contamination source independent of environmental soil levels, with stainless-steel evaporators driving nickel, zinc, and copper additions during the boiling stage.
Key numbers
Sampling (Table 1): Amherst MA: 6 sap, 3 syrup; Roselle NJ: 18 sap, 4 syrup; West Scranton PA: 8 sap, 4 syrup; West Hartford CT: 27 sap, 5 syrup. Total: 59 sap samples, 16 syrup batches.
Analytical method: Macroelements (aluminum, calcium, potassium, magnesium, sodium, iron) by Agilent 5110 ICP-OES; trace elements (arsenic, cadmium, cobalt, chromium, copper, nickel, lead, antimony, selenium, tin, thorium, uranium, zinc) by Agilent 7700x ICP-MS. Digestion: 0.5 g subsample in 30% H2O2 plus 9:1 HNO3:HCl at 70 degrees C for 60 minutes in closed tubes, diluted to 50 mL.
Detection limits: 0.01 ng/g for all trace elements (applies to sap and syrup digests).
Quality control: Procedural blanks below 0.01 ng/g for all trace elements; corn syrup spiked with Inorganic Ventures multielement standard 71-A, recovery 82 to 109%; duplicate CV below 11% for saps and syrups. Soil CRM: NIST 2709a San Joaquin Soil, recovery 81 to 113% of certified values. LOQ not stated separately from LOD.
Regulatory exceedances in finished syrup (text, pp. 4 to 5): Arsenic exceeded FDA regulatory limits at all four sites. Cadmium exceeded at all four sites. Nickel exceeded at all four sites. Zinc exceeded at all four sites. Lead exceeded at three sites (Amherst MA, West Hartford CT, West Scranton PA); Roselle NJ did not exceed despite having the highest soil lead concentration. Copper exceeded at one site only (Roselle NJ). The paper identifies the FDA food and EPA drinking-water combined regulatory line in Fig. 2 but does not restate the exact numeric thresholds in the text.
Concentration factors, sap to syrup (Conclusions, p. 5): Conservative tracer elements calcium, potassium, magnesium, sodium showed evaporative enrichment factors of 16 to 24, consistent with a 20:1 sap-to-syrup boil-down ratio. Cadmium: 1 to 7. Nickel: 5 to 16, reaching 29 to 38 at Roselle NJ, indicating net addition from stainless-steel equipment. Zinc: 2 to 38, with the same stainless-steel attribution at Roselle NJ. Copper: 2 to 29, with 29 to 38 at Roselle NJ from stainless steel. Arsenic: 1 to 3 (minimum enrichment). Lead: 0.5 to 1.7 (net partial loss during evaporation, attributed to adsorption on equipment surfaces and precipitating particles).
Evaporative enrichment summary: Cadmium, chromium, copper, nickel, and zinc increased 5 to 15 times from sap to syrup. Arsenic and lead increased only 1 to 2 times.
Concentration values: Exact mean or median concentrations per site per element are not stated in the paper text; they are presented in Fig. 2 as a log-scale bar chart. The figure would require digitization for precise ppb estimates. The order-of-magnitude ranges readable from Fig. 2 for finished syrup are approximately 0.001 to 0.1 ug/g for arsenic, lead, and cadmium; approximately 0.1 to 1 ug/g for nickel and copper; and approximately 1 to 10 ug/g for zinc. These are approximate from a log-scale figure and should not be treated as tabulated data.
Risk assessment: Total Hazard Quotients for all metals combined were below 1 (indicating acceptable risk) for adults and larger children at a typical consumption rate below 20 g/d. The Amherst MA syrup posed a risk to toddlers weighing approximately 10 kg at consumption above 4 g/d, driven primarily by arsenic and nickel in that batch.
Soil-to-plant correlation: Soil metal concentrations did not predict sap or syrup concentrations (R-squared below 0.20, p above 0.05 for most elements). Equipment materials were the dominant determinant of syrup composition for nickel, zinc, and copper.
Methods (brief)
Strong acid digestion of 0.5 g sap or syrup subsamples; ICP-OES for macroelements; ICP-MS for 13 trace elements. Soil digestion by US EPA Method 3050B (pseudototal fraction). LOD 0.01 ng/g. Recovery verified by spiked corn syrup and soil CRM. No speciation of arsenic species (total arsenic only). Chromium is total chromium, not hexavalent.
Evidence fitness
This source supports finished-product occurrence data for maple syrup, specifically the finding that all suburban syrup batches in this study exceeded FDA regulatory limits for total arsenic, cadmium, nickel, and zinc, and three of four exceeded the limit for lead. The sap-to-syrup concentration factors are stated in text and are reliable. Exact point estimates in ppb for each site and metal are not extractable from text alone; they require digitizing Fig. 2. The 16-sample set covers only northeastern suburban sites and is not nationally representative. No speciation of arsenic (total arsenic only); chromium is total, not hexavalent. This source does not support data on agave syrup, molasses, or corn syrup.
Limitations
Small sample size (16 syrup batches, 4 sites). Coverage limited to northeastern US suburban trees; commercial maple syrup operations differ in scale, equipment, and production geography. Data are in figures, not tables; exact concentration values per site are not available without figure digitization. Total arsenic only; inorganic arsenic not speciated. Chromium is total, not hexavalent. The paper does not state which exact FDA action levels or EPA MCLs constitute the “FDA/EPA regulatory line” in Fig. 2.
Related evidence
Update history
No substantive edit history is available in this build. The full commit record is available in git.