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The Screening-Level Evaluation of Contaminants in Sediments from Three Reservoirs and the Estuary of the Klamath River, 2009-2011 by CDM Smith and Stillwater Sciences identifies several toxins, referred to as Chemicals of Potential Concern (COPCs), in the sediments of Copco 1 and Iron Gate Reservoirs. These toxins were detected through sediment sampling and analysis, with some exceeding freshwater, marine, or human health screening levels, indicating potential ecological or health risks. Below is a comprehensive list of all toxins identified in the sediments of Copco 1 and Iron Gate Lakes, based on the document’s findings, particularly from Chapter 3 and associated tables (Tables 2, 3, 4, and 5).

Toxins in Copco 1 and Iron Gate Lake Sediments

Copco 1 Reservoir

The following toxins were detected in Copco 1 Reservoir sediments, with some exceeding screening levels for freshwater (Table 2), human health (Table 3), or marine environments (Table 4), or noted as significant in dioxin/furan Toxic Equivalency (TEQ) evaluations (Table 5):

• Toxic Heavy Metals:
  • Aluminum: Exceeded freshwater sediment screening levels (Table 2, p. 3-3).
  • Arsenic: Exceeded freshwater and human health screening levels (Tables 2 and 3, pp. 3-3, 3-8).
  • Chromium: Exceeded freshwater sediment screening levels (Table 2, p. 3-3).
  • Copper: Exceeded freshwater sediment screening levels (Table 2, p. 3-3).
  • Lead: Exceeded freshwater and human health screening levels (Tables 2 and 3, pp. 3-3, 3-8).
  • Nickel: Exceeded freshwater and human health screening levels (Tables 2 and 3, pp. 3-3, 3-8).
• Organic Toxins:
  • Dioxins and Furans: Detected and evaluated using Toxic Equivalency (TEQ) calculations, with levels contributing to potential ecological and human health concerns (Table 5, pp. 3-25–3-29). Specific congeners not listed but included in TEQ analysis.
  • Dioxin-like PCB Congeners: Contributed to TEQ calculations, indicating bio-accumulative potential (Tables 5–7, pp. 3-25–3-29).
  • DDT (Dichlorodiphenyltrichloroethane): Exceeded human health and marine sediment screening levels, noted as a persistent pesticide (Tables 3 and 4, pp. 3-8, 3-14).
  • PCBs (Polychlorinated Biphenyls): Exceeded human health screening levels, with dioxin-like congeners posing bioaccumulation risks (Table 3, p. 3-8).
  • PAHs (Polycyclic Aromatic Hydrocarbons): Specific compounds (e.g., Fluoranthene) detected, with some exceeding screening levels, contributing to ecological concerns (Table 2, p. 3-3).
  • Chlordane: Exceeded human health screening levels, noted as a persistent pesticide (Table 3, p. 3-8).

Iron Gate Reservoir

The following toxins were detected in Iron Gate Reservoir sediments, with some exceeding screening levels or noted in TEQ evaluations:

• Toxic Heavy Metals:
  • Aluminum: Exceeded freshwater sediment screening levels (Table 2, p. 3-3).
  • Arsenic: Exceeded freshwater and human health screening levels (Tables 2 and 3, pp. 3-3, 3-8).
  • Chromium: Exceeded freshwater sediment screening levels (Table 2, p. 3-3).
  • Copper: Exceeded freshwater sediment screening levels (Table 2, p. 3-3).
  • Lead: Exceeded freshwater and human health screening levels (Tables 2 and 3, pp. 3-3, 3-8).
  • Nickel: Exceeded freshwater and human health screening levels (Tables 2 and 3, pp. 3-3, 3-8).
• Organic Toxins:
  • Dioxins and Furans: Detected with TEQ contributions, indicating potential risks (Table 5, pp. 3-25–3-29).
  • Dioxin-like PCB Congeners: Included in TEQ calculations, with bioaccumulation concerns (Tables 5–7, pp. 3-25–3-29).
  • DDT: Exceeded human health and marine sediment screening levels (Tables 3 and 4, pp. 3-8, 3-14).
  • PCBs: Exceeded human health screening levels, with bio-accumulative properties (Table 3, p. 3-8).
  • PAHs: Detected, with some compounds exceeding screening levels (Table 2, p. 3-3).
  • Chlordane: Exceeded human health screening levels (Table 3, p. 3-8).

Additional Notes

• Screening Levels and TEQ Analysis: The document lists toxins exceeding freshwater (e.g., Effects Range Low, Probable Effect Concentration), human health (e.g., California Human Health Screening Levels), or marine (e.g., Effects Range Median) screening levels, indicating potential risks (Tables 2–4, pp. 3-3–3-14). Dioxins, furans, and dioxin-like PCBs were evaluated using TEQ calculations to assess cumulative toxicity, with results suggesting low but non-negligible risks (Section 3.5, pp. 3-22–3-27).
• Sediment Composition: Sediments in both reservoirs are 78% clay, which traps toxins, increasing bioaccumulation risks when disturbed, as noted in critiques of the 2024 dam removal (Siskiyou News, 2024).
• Context with WHFB: The WHFB’s rewilding plan, relocating horses to wilderness areas, could mitigate environmental impacts by reducing sediment disturbance risks compared to dam removal, aligning with concerns about toxin release (Wild Horse Fire Brigade, n.d.-b).
• Data Limitations: The document’s screening-level approach does not provide exact concentrations for all toxins, and some (e.g., specific PAH compounds) are generalized. Appendix A and Tables 2–4 provide the most detailed COPC lists, but further data (e.g., raw sediment concentrations) would require the full report’s appendices, not fully excerpted here.

Comprehensive List of Toxins

Combining the findings for both reservoirs, the toxins in Copco 1 and Iron Gate Lake sediments include:

• Toxic Heavy Metals:
  • Aluminum
  • Arsenic
  • Chromium
  • Copper
  • Lead
  • Nickel
• Organic Toxins:
  • Dioxins and Furans
  • Dioxin-like PCB Congeners
  • DDT (Dichlorodiphenyltrichloroethane)
  • PCBs (Polychlorinated Biphenyls)
  • PAHs (Polycyclic Aromatic Hydrocarbons, e.g., Fluoranthene)
  • Chlordane

Sources

• CDM Smith & Stillwater Sciences. (2011). Screening-Level Evaluation of Contaminants in Sediments from Three Reservoirs and the Estuary of the Klamath River, 2009-2011. Prepared for U.S. Department of the Interior. (Tables 2–7, pp. 3-3–3-29; Section 3.5, pp. 3-22–3-27).
• Siskiyou News. (2024). Possible issues with the Klamath Dam removal project. Retrieved from https://www.siskiyou.news/2023/11/22/possible-issues-with-the-klamath-dam-removal-project/
• Wild Horse Fire Brigade. (n.d.). About WHFB. Retrieved from https://www.wildhorsefirebrigade.org/about