# Polychlorinated Alkane Profiles and Concentrations in Bolivian Andes Soils Point to a Long-Range Transport Influence

## TL;DR

Pollutants in high-altitude Bolivian soils suggest long-range atmospheric transport from distant sources.

## Contribution

The study reveals how pollutants reach remote high-altitude areas via atmospheric transport.

## Key findings

- PCA concentrations in urban soils decreased with distance but increased again above 4,700 masl.
- Forensic fingerprints and isotope signatures support long-range transport as a pollutant source.
- High-altitude areas show pollutant levels comparable to urban centers, highlighting transport efficiency.

## Abstract

High-altitude terrain
may intersect the upper atmospheric
boundary
layer and exhibit distinct environmental dynamics. We investigated
the anthropogenic pollutants polychlorinated alkanes (PCAs, also known
as chlorinated paraffins) in surface soils along a transect from the
La Paz-El Alto metropolitan area in Bolivia (3200–4100 masl)
to the upper slopes of Mount Chacaltaya (>5200 masl), around 16
km
away. Concentrations of PCAs in urban soils (750–5,230 ng/g
organic carbon [OC]) decreased exponentially with increasing distance
from the urban boundary, declining to ∼150 ng/g OC at elevations
below 4,700 masl. Beyond 4,700 masl concentrations increased again,
reaching levels comparable to those in the urban area, 1,670–4,300
ng/g OC, above 5,000 masl. Given that pollutant concentrations typically
decline with distance from their source, this altitudinal trend, together
with a pronounced shift in PCA forensic fingerprints near 4,700 masl,
strongly suggests contributions from sources beyond the local metropolitan
area. Carbon and nitrogen isotope signatures in organic carbon further
support long-range transport as a source, consistent with previous
modeling and observations that the upper slopes of Mount Chacaltaya
predominantly receive air masses and organic carbon from distant regions
via transport in the free troposphere. Our observation that pollutant
levels in high-altitude areas are comparable to those in the metropolis
of 1.8-million inhabitants underscores the efficiency of long-range
atmospheric transport.