Current practices underestimate environmental exposures to methamphetamine: inhalation exposures are important

The study addresses whether current assessment practices for methamphetamine-contaminated properties underestimate human exposure by ignoring the inhalation pathway. Although guidelines typically assume methamphetamine residues remain on surfaces and primarily cause dermal and ingestion exposures, evidence suggests methamphetamine can partition into indoor air as free base or adhere to aerosols/particles. The paper aims to evaluate whether methamphetamine present on indoor materials moves into the air phase at levels relevant to human inhalation exposure, and to assess whether commercially available air sampling and analytical methods can reliably quantify such exposures. The context includes widespread contamination from clandestine manufacture or smoking, reported adverse health effects among residents, and existing guidelines that exclude inhalation based on assumptions about volatility.

Previous work has shown methamphetamine in air during controlled clandestine manufacturing and smoking events, with reported concentrations up to 42 µg/m³ during cooking, 5500 µg/m³ during salting out and immediately post-cook, and 210 µg/m³ 24 h post-manufacture; smoking events yielded 300–1600 µg/m³. These studies typically used acid-treated glass fiber filters and GC-MS or LC-MS, characterizing aerosols rather than true vapor phase. The Minnesota Pollution Control Agency distinguished particulate/aerosol versus vapor phases by sequential filtration and acid-treated silica gel sorbent tubes analyzed by LC-MS. Solid phase microextraction (SPME) and capillary microextraction (CME) methods have trapped methamphetamine vapors from indoor environments, reporting 0.2–3 µg/m³ in suspected former labs when surface residues exceeded 40 µg/100 cm². However, these techniques require rapid analysis (≤5 days) and are not commercially available for routine indoor air sampling. Overall, while methamphetamine in indoor air has been documented, there is limited data from real-world, previously contaminated residences long after manufacture/use, and a need for practical, validated, commercially accessible methods.

Air sampling used commercially available ORBO-49P (OVS) Supelpak 20 tubes packed with treated Amberlite XAD-2 resin, suitable for sampling semi-volatile organics in both vapor and aerosol phases. Sampling employed calibrated SKC Airchek Sampler PCXR4 pumps at approximately 1 L/min, with total volumes <480 L following NIOSH 5601 and OSHA 62 guidance. Quality assurance included field blanks (FB), internal standard recoveries (ISR), laboratory control samples (LCS), laboratory spikes (LS), field spikes, and a laboratory method blank (LB). Tubes were analyzed by Eurofins (Brisbane) using an LC-MS/MS method based on NIOSH 9111 for meth/amphetamine-type compounds used for wipes, adapted for air tube extracts. Extraction used 0.1 M sulfuric acid in methanol with vortexing of XAD-2 resin 3–5 min and dilution to 30 mL methanol. Deuterated internal standards (d5-amphetamine·HCl, d5-methamphetamine·HCl, d5-MDMA·HCl, d5-MDA·HCl, d3-ephedrine) were added prior to extraction; blank ORBO tubes were spiked with native analytes to assess recovery. Field spikes were prepared with 1.5 µg deuterated standards and taken to the field. Maximum holding time was 30 days. LC-MS/MS utilized an Agilent 1290 UHPLC with Agilent 6460/6470 triple quadrupole (positive-ion MRM), with separation on Phenomenex Kinetex Biphenyl (3.0×50 mm, 2.6 µm) or Agilent ZORBAX Eclipse Plus C18 (2.1×50 mm, 1.8 µm). Calibration levels: 0.002, 0.024, 0.150, 0.302, 1.465, 3.018 µg; upper limit 3.018 µg, with dilution as needed. Method detection limits (MDLs): 0.0002 µg (methamphetamine), 0.0003 µg (amphetamine), 0.0001–0.0004 µg across analytes; lower limits of reporting (LLOR) = 3.14×MDL; target LOR 0.02 µg for all six analytes. Measurement uncertainty (k=2) ~20.2–23.9%; precision 1.7% (methamphetamine) to 8.2% (ephedrine); accuracy 86% (ephedrine) to 109% (MDMA). No detections in FB or LB; LCS/LS recoveries generally 93–124% (methamphetamine 103–112%; amphetamine 102–109%); field spikes recoveries 84–103% (methamphetamine) and 74–108% (amphetamine); surrogate recoveries on samples generally 70–130%. Field sampling: Two Australian locations. House 1 (urban residence) suspected prior manufacture; residents lived 9 years with reported illness; surface residues 0.52–49 µg/100 cm² (average 12.6 µg/100 cm² across contact surfaces), with 250 µg/100 cm² on an air conditioner front panel. House vacant, not remediated. Air samples collected at multiple locations with air conditioner on/off, including dining table under AC (AC on/off), children’s room (furthest from AC; AC on/off), and kitchen/playroom doorway adjacent to dining. Sample volumes 132–286 L. House 2 (rural residence) known prior manufacture; residents 2 years with reported illness; wall residues 0.54–110 µg/100 cm² (average 31 µg/100 cm²). During remediation setup, samples collected from: a ventilated shipping container holding hard items from a shed; sealed bag of soft toys from the home (two time points, T1 and T2); sealed bag of soft foam materials (SM). Sample volumes 88–144 L (Feb) and 115 L (Apr for field-spiked tubes).

• Methamphetamine was detected in every air sample; amphetamine in several samples. Pseudoephedrine, ephedrine, MDMA, and MDA were not detected in air.
• House 1 air concentrations (methamphetamine, amphetamine in µg/m³): • H1-IAD (dining under AC, AC on): 0.53 meth; 0.013 amph • H1-IADX (dining under AC, AC off): 4.5 meth; 0.29 amph • H1-IAKX (children’s room, AC off): 3.8 meth; 0.20 amph • H1-IAK (children’s room, AC on): 6.2 meth; 0.21 amph • H1-IAP (kitchen/playroom doorway, AC on): 8.3 meth; 0.30 amph
• House 2 air concentrations (µg/m³): • H2-C (ventilated container with hard items): 0.008 meth; amphetamine not detected • H2-T1 (sealed bag soft toys): 0.046 meth; amphetamine not detected • H2-T2 (sealed bag soft toys; field-spike-prepared tubes, Apr): 0.30 meth; 0.013 amph • H2-SM (sealed bag soft foam): 0.0016 meth; 0.0087 amph
• Concentrations spanned three orders of magnitude across locations and conditions, demonstrating substantial potential for inhalation exposure in contaminated environments and from contaminated possessions.
• QA/QC performance indicated acceptable analytical reliability: no blank contamination; LS/LCS 93–124%; field spikes largely within expected ranges; surrogate recoveries mostly 70–130%.
• Analytical performance: MDLs as low as 0.0002 µg (methamphetamine), target LOR 0.02 µg; measurement uncertainty ~20–24%; precision and accuracy within acceptable bounds.

Findings demonstrate that methamphetamine readily partitions from contaminated building materials and possessions into the indoor air phase, providing both an inhalation exposure route and a mechanism for contaminant redistribution within properties long after manufacture or use has ceased. Air concentrations measured in an unremediated home with substantial surface contamination reached 0.53–8.3 µg/m³, while contaminated items stored in containers or sealed bags also emitted measurable methamphetamine (≤0.30 µg/m³). The presence of amphetamine in some air samples supports degradation or co-contamination pathways. These results directly challenge the prevailing assumption underlying many risk-based guidelines that methamphetamine remains confined to surfaces and that inhalation exposures are negligible, especially post-remediation. Laboratory and prior studies support the dynamic exchange between gypsum wallboard and air, consistent with the observed air-phase methamphetamine. Incorporating inhalation into exposure assessments is therefore necessary to avoid underestimation of total intake (which also includes dermal and ingestion pathways) and to better protect public health. The study further shows that commercially available sorbent tube methods with LC-MS/MS analysis can reliably quantify methamphetamine in indoor air, enabling practical routine assessment.

The study establishes that inhalation is a significant and previously underappreciated exposure pathway for methamphetamine in contaminated residential environments. Methamphetamine can volatilize/desorb from building materials and possessions into indoor air at measurable levels, potentially leading to substantial inhalation intake and facilitating contaminant transport within properties. Current guidelines that exclude inhalation likely underestimate total exposure and may not be protective of health. Commercially available XAD-2 sorbent tube sampling coupled with LC-MS/MS provides a practical, validated approach for routine indoor air measurements of methamphetamine. Future work should: (1) quantify inhalation exposure across a wider range of real-world settings and post-remediation scenarios; (2) characterize temporal variability and the influence of HVAC operation and environmental conditions; (3) refine exposure models and risk-based guideline values to explicitly include inhalation; and (4) investigate emission dynamics from various materials and contents to guide effective remediation and clearance criteria.

• Limited number of study locations (two properties) and samples restricts generalizability.
• Variable access times constrained sample volumes and duration; temporal variability could not be fully characterized.
• Homes differed in status (unremediated vs. during remediation) and sampling contexts (rooms vs. stored contents), limiting direct comparability.
• While method QA/QC was acceptable, some surrogate recoveries were slightly outside the typical 70–130% range.
• Phase partitioning (vapor vs. aerosol) was not explicitly differentiated by the selected method; results represent total air-phase capture on XAD-2 OVS tubes.