SD3 - Report on the Toxicity of Selenium to Aquatic Life (SJR 35, 2014 and HJR 57, 2014)
Selenium is a naturally occurring element present in soils in varying amounts depending on local geology. Although selenium is a micronutrient needed by animals in small amounts for proper cellular function, excess levels can cause toxic effects, with fish being especially sensitive. Selenium toxicity in contaminated aquatic ecosystems is especially complex and it can cause adverse impacts in a different manner than most other toxic substances.
Under the Federal Clean Water Act, section 304(a) requires the U.S. Environmental Protection Agency (EPA) to develop water quality criteria based on available scientific information. EPA requires States to consider EPA’s recommendations (40 CFR Part 131) when adopting water quality criteria into their water quality standards. For toxic substances, water quality criteria are the numerical concentrations that if not exceeded should protect aquatic life. EPA develops water quality criteria based on available scientific information and publishes their recommended criteria for States to use in adopting criteria. Once a State adopts water quality criteria into their water quality standards, EPA must approve them before they become effective.
The science of selenium toxicity has been developing and evolving over several decades, with EPA first issuing recommended water quality criteria for selenium in 1980, with revised criteria issued in 1987. These 1987 recommendations were adopted into Virginia’s Water Quality Standards Regulation (9 VAC 25-5 through -550) and are still in force:
1. 20 ìg/L (micrograms per liter; parts per billion) for the acute criterion (short term exposures), and
2. 5 ìg/L for the chronic criterion (long term exposures)
After EPA issued their 1987 selenium criteria, toxicologists continued to discover additional complexities in the way selenium causes adverse affects in the environment and EPA has been actively studying the toxicity of selenium since the mid-1990s, with the intent to revise their 1987 recommended criteria. Most recently, in May 2014 EPA announced the availability of a new draft Aquatic Life Criteria Document for Selenium in Freshwater, prepared for public review as well as an external peer review. In addition, some States have been considering revisions to their selenium water quality criteria, notably Kentucky, which proposed revisions over the last couple of years that have been partially approved by EPA and contested by environmental groups through lawsuits.
EPA’s latest recommendations are for chronic criterion concentrations, intended to protect against long term exposures because of the fact that selenium acts in a bioaccumulative manner. EPA is not recommending an acute criterion. EPA’s recommended criteria include four different elements:
1. A fish egg-ovary dry weight concentration of 15.2 mg/kg (milligrams per kilogram; parts per million).
2. Fish-tissue dry weight concentration of 8.1 mg/kg in whole fish, or 11.8 mg/kg dry weight in fish filet.
3. A water concentration – either 4.8 ìg/L in lotic water (running water in streams and rivers) or 1.3 ìg/L in lentic waters (still waters in lakes and impoundments).
4. A formula for calculating a water criterion for short term or intermittent exposures.
EPA recommends that States adopt all four elements and that the egg-ovary element takes primacy over all other elements and the whole body or filet tissue element takes precedence over the water column elements. This will allow for some flexibility in monitoring and assessment.
Because of the controversy over Kentucky’s proposed revisions to their selenium criteria and the preliminary nature of EPA’s most recent recommendations, DEQ recommended (with State Water Control Board approval in March 2014) that revisions to Virginia’s selenium criteria not be included as part of DEQ’s 2014 Triennial Review of water quality standards. However, as directed by SJ35 and HJ57, DEQ has reviewed the current state of the science on selenium toxicity to aquatic life and recommends that once EPA finalizes their recently proposed criteria for selenium, DEQ should consider initiating a rulemaking to amend Virginia’s current water quality criteria for selenium.