A Comparison of Toxicology Studies of Vulnerability of Early Life Stages of Salmon to Hexavalent Chromium at Hanford-14140

Laboratory and field ecotoxicology studies clarify levels of pollutants that adversely affect organisms at various life stages. We examined three well-controlled laboratory studies of hexavalent chromium (Cr-VI) toxicity to fertilization, eggs and juvenile Chinook Salmon (Oncorhynchus tshawytscha), to identify effect levels for several endpoints. These studies are relevant to Cr-VI contamination of ground and surface water. At the Department of Energy’s Hanford Site, ground water with chromium flows towards the Columbia River, upwelling through the gravel (pore water) into the river, posing a potential threat to biota, including the eggs and newly hatched salmon. Three ecotoxicological studies assessed fertilization and hatching [1], and pathophysiology, growth, and survival of alevin [2] and parr [3] eggs and young salmon. Farag et al. [1,3] used salmon eggs from a remote hatchery to avoid any possible evolutionary adaptations to chromium and used deionized water spiked with chromate to minimize effects of other ground water constituents. Patton et al. [2] used salmon eggs from nearby Priest Rapids hatchery to incorporate possible adaptation to historic exposures, and used chromate-rich Hanford ground water diluted with Columbia River water to achieve natural exposure conditions. Both choices were justifiable, but since the three studies tested different life stages, the methodological implications for toxicology and exposure, have not been tested on a particular life stage. Farag et al. [1] studied fertilization and hatchability on the one hand and freeswimming parr on the other, while Patton et al. tested the alevin stage, during which the newly hatched fish remain in gravel exposed to pore water, and do not feed. Fertilization, hatching, and alevin survival were not reduced at 260-266 μg/L (ppb) of Cr-VI in the water (=NOAEL for eggs and alevins). Older fish (parr) had metabolic and histologic changes of uncertain significance at levels as low as 24 ppb, but this stage does not encounter levels above 10 ppb in the rapidly flowing river water. LOAELs for some endpoints were 100-120 μg/L. At 266 μg/L, 1 WM2014 Conference, March 2 – 6, 2014, Phoenix, Arizona, USA survival was significantly reduced for parr (97% to 70%), but there was no survival effect for the alevin. These results suggest that Cr-VI in Hanford pore water are too low to impact Chinook Salmon populations. Funded by the DOE through a contract to Consortium for Risk Evaluation with Stakeholder Participation (CRESP-DE-FG-26-00NT-40938). INTRODUCTION Salmon are iconic wildlife species of the Pacific Northwest. Salmon, wild and farmed, rank third in the United States per capita seafood consumption, behind shrimp and canned tuna [4]. The several species of wild salmon spawn in the gravel beds of freshwater streams and rivers, requiring clear, well-oxygenated flows. After hatching the juvenile salmon pass through several stages (alevin, fry, parr, smolt). The young salmon (as parr) migrate downstream to estuaries and, as smolt enter the sea. After several years maturing at sea, the adults return to spawn in their natal streams. Wild salmon populations support huge commercial and recreational fisheries, and salmon are a vital and historic part of the culture and diet of Northwestern Tribes [5]. Salmon populations in the Columbia River have fluctuated dramatically over the past 70 years [6], with an overall decline [7]. Salmon populations have been heavily impacted by fishing, by dams that interfere with upriver and down river migration [8], and by development diminishing suitable spawning sites. There is also concern about the possible negative impact of environmental contaminants on the health of individual salmon and salmon populations. Chinook (or King) Salmon (Oncorhynchus tshawytscha) populations and ‘runs’ in various rivers are listed as endangered or as a species of special concern. The species has a complicated and variable life cycle [9]. Adult fish spend several (up to 8) years at sea, before migrating upriver to spawn. The life stages include eggs laid in gravel nests called redds, alevin that remain in the gravel for weeks, becoming fry after “swim-up”. Fry become parr after about 10 weeks, and finally smolt that enter the sea [9]. Eggs take up to three months to hatch. Alevins (recently-hatched fish) remain in the gravel for several weeks, absorbing their yolk sac. They do not eat. Fry are young fish that have just emerged from the redds after “swim-up”; they eat voraciously. Parr grow rapidly through the fingerling stage, and most migrate downriver to the estuaries. The Columbia River is subject to natural seasonal variation in water height and current velocity, which is significantly modified by water release practices at the dams [8]. The Hanford Reach (about 80 km) between Priest Rapids Dam and Richland city, is the largest “natural” stretch remaining on the Columbia River, and is an important spawning ground for the fall run Chinook Salmon. The nine deactivated plutonium-production reactors are arrayed along the Hanford Bight (the northernmost point of the Hanford Reach). Here, hexavalent chromium (Cr-VI), formerly used to control corrosion in the reactor cooling water, is now a contaminant of ground 2 WM2014 Conference, March 2 – 6, 2014, Phoenix, Arizona, USA water, with several documented plumes. As the Cr-VI groundwater plumes move toward the Columbia River they reach the gravel riverbed. Some of the ground water seeps out along the shoreline under low-flow conditions, and some occurs as upwellings through the gravel riverbed (hyporheic zone). The continued movement of the Cr-VI plume eventually enters the freeflowing river where it is rapidly diluted and carried downstream. The key aspects of the Chinook Salmon life history that makes it vulnerable to chemicals in groundwater (including chromium) are the time spent in the gravel as eggs or alevin (exposed to groundwater upwellings called ‘pore water’), and the time spent as fry or parr probably feeding close to the gravel, where they might be exposed to chromium in water or from the food chain. The current Washington State Ambient Surface Water Criteria for chronic exposure to hexavalent chromium is 10 μg/L (=10 ppb), while the Environmental Protection Agency (EPA) chronic ambient water quality criterion for chromium is 11 μg/L. The standard applies equally to total chromium and hexavalent chromium (Cr-VI)(see below). The drinking water standard for chromium is 100 μg/L, and a separate standard for Cr-VI in drinking water is currently under development [10]. Chromium concentrations in the river, itself, are typically below any detection level, but in the pore water, levels occasionally exceed 100 μg/L. Porewater samples analyzed along the Hanford Reach contained an average of 20 μg/L in 1995 (n=141 samples) and 15 μg/L in 2009 (n=124 samples). The maximum concentration was 632 μg/L. Hence it can be important to understand what levels of Cr-VI in pore water would harm the eggs and alevin. The Washington Department of Ecology’s [11] current position is that “Research to date shows no negative impact to salmon from chromium concentrations.” The authors of the ecotoxicological studies examined here, concur that the value of 10 μg//L [1-3] hereinafter referred to as Farag studies and Patton study) would be protective of salmon, both directly and indirectly by protecting the food chain on which the juvenile salmon depend. The Farag and Patton studies were conducted in the 1990s. Dauble et al. [12], provided a detailed methodological summary of Farag and Patton studies and results (prior to their peerreview publications), and concluded that exposure up to 266 μg/L showed no effect on fertilization rate, viable hatch, growth or survival. The present paper examines the three studies with respect to effect levels. METHODS We examined three laboratory studies of the impact of Cr-VI on early life stages of Chinook Salmon. We looked for evidence relevant to LOELs (lowest observed effect levels) and LOAELs (lowest observed adverse effect levels). In some cases, authors may document