Why is there arsenic in Great Salt Lake?

The Great Salt Lake, one of North America’s most unique and ecologically vital lakes, is not only known for its salinity and biodiversity, but also for containing naturally occurring arsenic. The presence of arsenic—a toxic element often associated with industrial pollution—raises concerns among scientists, conservationists, and policymakers. However, unlike some water bodies where arsenic is mostly a result of human contamination, much of the arsenic in the Great Salt Lake is natural, although human activity can influence how it behaves and spreads.

Natural Geologic Sources of Arsenic

The primary reason arsenic is found in the Great Salt Lake is due to geological factors. Utah’s geology includes arsenic-bearing minerals in sedimentary and volcanic rocks. As groundwater and surface water move through these mineral-rich deposits, arsenic leaches out and is carried by rivers into the Great Salt Lake.

The major tributaries to the lake—the Bear, Weber, and Jordan Rivers—drain regions that pass through rock formations containing arsenopyrite, realgar, and other arsenic-bearing minerals. These rivers transport dissolved arsenic into the lake where it becomes part of the lake's chemical composition.

The Role of the Jordan River and Urban Runoff

Among the tributaries, the Jordan River is a notable contributor of arsenic to the Great Salt Lake. It flows from Utah Lake through Salt Lake Valley—a highly urbanized and industrialized area. Along its route, the river picks up runoff from agricultural fields, urban streets, and old mining districts. Some of this runoff contains arsenic from both natural soils and legacy contamination, such as mining tailings and industrial discharge sites.

Additionally, stormwater runoff and wastewater treatment plants can elevate the levels of arsenic and other metals in the river, particularly during heavy rain events.

Lake Chemistry and Arsenic Mobility

Once arsenic reaches the Great Salt Lake, its behavior is shaped by the lake’s unique chemistry. The Great Salt Lake is hypersaline, alkaline, and rich in other dissolved ions like sulfate, chloride, and carbonate. These conditions affect how arsenic exists in the water—either as a soluble form (arsenate or arsenite) or bound to particles and sediments.

The high pH and salinity of the lake increase the mobility of arsenic, allowing it to remain dissolved in the water rather than settling in sediments. This contributes to its persistence in the lake and availability for biological uptake or chemical reactions.

Human Activities and Arsenic Cycling

While the arsenic in the Great Salt Lake largely originates from natural sources, human activities influence its concentration, distribution, and risk:

1. Water diversions for agriculture and urban use reduce freshwater inflows, altering the lake's salinity and concentrating dissolved substances like arsenic.
2. Mining and mineral extraction in the watershed—especially historical mining in the Oquirrh Mountains and around Bingham Canyon—have left behind arsenic-rich tailings and waste piles.
3. Industrial evaporation ponds on the lake’s margins may also concentrate arsenic from brines used in mineral harvesting operations.

These actions may not introduce arsenic directly, but they can alter the lake’s hydrology and chemistry, affecting how arsenic moves and accumulates.

Ecological and Health Concerns

Arsenic in the Great Salt Lake poses potential risks to both wildlife and humans, although the full extent of these risks is still being studied. Key concerns include:

1. Bioaccumulation in brine shrimp and other invertebrates, which form the base of the food chain for millions of migratory birds.
2. Possible transfer of arsenic through the food web, affecting bird species such as phalaropes, eared grebes, and American avocets.
3. Human exposure through dust: As lake levels drop, exposed lakebed sediments can become airborne, potentially containing arsenic that may pose respiratory health risks to nearby communities.

In recent years, researchers and public health agencies have become increasingly concerned about dust storms from the drying lake. If arsenic-laden sediments are picked up by wind, they could contribute to air pollution and chronic health issues along the Wasatch Front.

Ongoing Research and Monitoring

The Utah Department of Environmental Quality (DEQ), in coordination with academic researchers and conservation groups, is actively monitoring arsenic levels in:

• Water and brine
• Sediments
• Dust particles
• Wildlife tissues

This research is essential to understand how climate change, prolonged drought, and human water use are intensifying arsenic-related risks.

In 2022 and 2023, scientists sounded alarms as the lake hit historic low levels, further exposing sediments and concentrating pollutants. Their work is crucial for informing policy decisions aimed at preserving the health of the lake and the communities around it.

Conclusion

Arsenic is present in the Great Salt Lake primarily due to natural geologic processes, but its behavior and impact are shaped by human activity and environmental changes. With lake levels declining and more lakebed exposed, arsenic poses growing ecological and public health concerns. Understanding and managing arsenic in the Great Salt Lake requires a combination of scientific research, careful monitoring, and sustainable water policy to ensure the long-term health of this iconic inland sea.