Service Area

Ecological Risk

Regulations that protect our natural resources increasingly emphasize the need to evaluate risks to the environment.  Ecological risk assessment has evolved into an important decision-making framework for the management and development of site remediation strategies, as well as the development and marketing of new products, drugs, and technologies.  The assessment of ecological risks has also become an integral part of corporate governance and sustainability goals.  Gradient is widely recognized as one of the nation’s premier risk assessment firms, with exceptional skills in ecotoxicology, ecological exposure modeling, and quantitative ecological risk analysis.

Our Ecological Risk Expertise Includes:

  • Natural resource damage (NRD) support
  • Integrated ecological and human health risk-based remedial solutions
  • Site-specific ecological risk assessment
  • Design, oversight, and interpretation of environmental fate and ecotoxicity studies
  • Scientific and regulatory comment
  • Product/chemical environmental safety assessment
  • Causation analysis
  • Ecological hazard and risk-based sustainability initiatives

Example Publications:

Fairbrother, A; Muir, D; et al. 2019. “Toward sustainable environmental quality: Priority research questions for North America.” Environ. Toxicol. Chem. 38(8):1606-1624.

Wait, D; Verslycke, T. 2019. “Expert Insight: Uniform data quality ecotoxicity assessment.” In Natural Resource Damages: A Guide to Litigating and Resolving NRD Cases (Eds: Israel, BD; Marston, B; Daniel, L), American Bar Association, Chicago, IL. p213-215.


Marty, MS; Blankinship, A; Chambers, J; Constantine, L; Kloas, W; Kumar, A; Lagadic, L; Meador, J; Pickford, D; Schwarz, T; Verslycke, T. 2017. “Population-relevant endpoints in the evaluation of endocrine-active substances (EAS) for ecotoxicological hazard and risk assessment.” Integr. Environ. Assess. Manag. 13(2):317-330.

Mayfield, DB; Johnson, MS; Burris, JA; Fairbrother, A. 2014. “Furthering the derivation of predictive wildlife toxicity reference values for use in soil cleanup decisions.” Integr. Environ. Assess. Manag. 10:358-371.

Verslycke, T; Reid, K; Bowers, T; Thakali, S; Lewis, A; Sanders, J; Tuck, D. 2014. “The Chemistry Scoring Index (CSI): A hazard-based scoring and ranking tool for chemicals and products used in the oil and gas industry.” Sustainability 6:3993-4009.

Sample Projects

Critical Area Ordinance for Wetlands and Fish and Wildlife

Gradient prepared comments on proposed changes to critical area ordinances for wetlands and fish and wildlife habitat conservation areas in a western state.  Our comments focused on the consistency of the proposed changes with existing regulations and regulatory guidance, the use of best available science, and the need for and effectiveness of the proposed measures.

Regulatory Comment on Effluent Limits for Electric Power Generation

Gradient critically reviewed the technical materials supporting proposed effluent limit guidelines (ELGs) under the Clean Water Act for steam electric power generation utilities.  US EPA proposed ELG changes for several parameters, including arsenic, selenium, and mercury.  We assessed the completeness and validity of the analyses performed by US EPA to support the rule-making effort, including considerations of toxicity, fate and transport in the environment, and cost analysis of potential impoundment failure risks.

Ecological Injury Assessment and Causation Analysis

Gradient has conducted ecological injury assessments and causation analyses for terrestrial and aquatic wildlife receptors exposed to a variety of chemicals at different industrial sites.  In several instances, we provided expert testimony.

Alternative Concentration Limits for the Protection of Aquatic Organisms

Gradient evaluated technical approaches for developing alternate concentration limits (ACL) for groundwater to surface water discharge from a chemical manufacturing facility located next to a large river.  We evaluated the relative sensitivity of benthic versus pelagic aquatic organisms for key chemicals of concern at the site, and reviewed current state of the science on mixing of groundwater with surface water in the hyporheic zone.

Natural Resource Damage Settlement Evaluation

Gradient evaluated the basis for a proposed natural resource damage (NRD) settlement offer at a Great Lakes Superfund site.  Using benchmarking analysis techniques, we quantitatively compared NRD settlements at other sediment sites to our client’s offer.  Our analysis considered the nature and extent of the ecological harm, as well as the role of our client’s releases in causing the harm.  Our work aided settlement negotiations.

Ecologically Based Polychlorinated Biphenyl (PCB) Cleanup in a River

Gradient conducted an ecological risk assessment for direct polychlorinated biphenyl (PCB) contact and dietary exposure to PCBs via the food web in fish, aquatic invertebrates, plants, mammals, and birds.  We developed “surface area weighted average” chemical intakes based on receptor foraging.  With this approach, we developed a site-specific remedial action goal for sediments.

Our Team