4-Nonylphenol in Sierra Nevada glaciers, California, USA

Importance of the topic

Persistent organic pollutants such as 4-nonylphenol (4NP) pose a threat to aquatic ecosystems and human health through endocrine disruption. Glaciers act as cold-storage reservoirs, accumulating atmospheric contaminants over decades before releasing them during melt cycles. Understanding how much 4NP is stored in glacial ice and snow, and predicting its future release, is key for downstream water quality management in a warming climate.

Objectives and study overview

• Quantify the total mass of 4NP in two Sierra Nevada glaciers: Palisade and Middle Palisade.
• Characterize spatial distribution of 4NP across glacier surfaces and depths.
• Estimate meltwater concentrations and assess downstream risk.

Methodology and instrumention

• Airborne LiDAR surveys (NASA Airborne Snow Observatory) collected snow‐on (2018) and snow‐off (2014) surface data to derive snow volume and glacier thickness via DEM differencing.
• GIS‐based “topographic shielding index” combined slope, elevation difference, and wind direction to estimate horizontal concentration gradients.
• Field sampling: Snow cores (1 ± 0.2 m depth) and meltwater grab samples collected in triplicate at representative glacier sites in 2018–2019.
• Laboratory analysis: Hexane liquid–liquid extraction, Kuderna–Danish concentration, and GC–MS (ion trap MS, splitless injection) using characteristic m/z 107, 121, 135, 149, 163.
• Density model: Seasonal snow (625 ± 70 kg/m³), transitional firn (depth‐dependent compaction model to 15–20 m), and glacier ice (917 kg/m³) used to partition glacier layers.
• Mass model: Layer volumes × density × 4NP concentration (predicted from shielding index for inaccessible areas).

Main results and discussion

• Snow water concentrations ranged 0.0063–0.10 mg/L on Palisade and 0.0023–0.077 mg/L on Middle Palisade, inversely correlated with topographic shielding (R²≈0.90).
• Meltwater concentrations were 6.1 ± 1.3 μg/L (Palisade) and 1.3 ± 0.05 μg/L (Middle Palisade), reflecting particulate filtration and older ice dilution.
• Total 4NP mass: Palisade = 3,974 ± 970 kg (3,456 ± 843 kg/km²); Middle Palisade = 582 ± 196 kg (1,677 ± 560 kg/km²).
• Most 4NP was stored in the transitional firn layer (564 ± 196 kg at Middle Palisade; 3,771 ± 970 kg at Palisade), representing decades of accumulation.
• Seasonal snow contained an additional ~15–17 kg per glacier; deep ice held minor mass, indicating limited pre-industrial deposition.

Benefits and practical applications of the method

• Combines high-resolution LiDAR and GIS for accurate pollutant vol­ume estimation across complex terrain.
• Topographic shielding index enables prediction of contaminant concen­tration in unsampled glacier areas.
• Framework applicable to other persistent organic pollutants and mountain ranges with consistent wind patterns.

Future trends and potential applications

• Climate-driven glacier retreat will accelerate remobilization of stored POPs, increasing downstream exposure.
• Ice-core studies could reconstruct historical 4NP usage trends and confirm model assumptions on deep-layer accumulation.
• Expansion to multimedia environmental fate models to evaluate air–snow–soil–surface water cycling of 4NP and related compounds.
• Adaptation of the LiDAR–GIS workflow for monitoring other emerging contaminants in seasonal snowpacks and glacial systems.

Conclusion

This study provides the first quantitative estimate of 4NP mass stored in two Sierra Nevada glaciers, revealing significant secondary pollutant reservoirs with potential to impact downstream ecosystems. The integrated LiDAR–GIS–chemical analysis approach offers a scalable method for assessing long-term pollutant fluxes from cryospheric sources under ongoing climate warming.

References

1. Lyons R, Lay J, Ivey J. 2020. 4-Nonylphenol in Sierra Nevada glaciers, California, USA. Arctic, Antarctic, and Alpine Research 52(1):222–235. DOI:10.1080/15230430.2020.1747758.