Glyphosate, aminomethylphosphonic acid (AMPA), imazapyr, sulfometuron methyl (SMM), and metsulfuron methyl (MSM) were measured in streamwater collected during and after a routine application of herbicides to a forestry site in Oregon's Coast Range. Samples were collected at 3 stations: HIGH at the fish-no-fish interface in the middle of the harvest and spray unit, MID at the bottom of the unit, and LOW downstream of the unit. All herbicides were applied by helicopter in a single tank mix. AMPA, imazapyr, SMM, and MSM were not detected (ND) in any sample at 15, 600, 500, and 1000ng/L, respectively. A pulse of glyphosate peaking at approximately equal to 62ng/L manifested at HIGH during the application. Glyphosate pulses peaking at 115ng/L (MID) and 42ng/L (HIGH) were found during the first 2 postapplication storm events 8 and 10 days after treatment (DAT), respectively: glyphosate was less than 20ng/L (ND) at all stations during all subsequent storm events. All glyphosate pulses were short-lived (4-12h). Glyphosate in baseflow was approximately equal to 25ng/L at all stations 3 DAT and was still approximately equal to 25ng/L at HIGH, but ND at the other stations, 8 DAT: subsequently, glyphosate was ND in baseflow at all stations. Aquatic organisms were subjected to multiple short-duration, low-concentration glyphosate pulses corresponding to a cumulative time-weighted average (TWA) exposure of 6634ng/Lxh. Comparisons to TWA exposures associated with a range of toxicological endpoints for sensitive aquatic organisms suggests a margin of safety exceeding 100 at the experimental site, with the only potential exception resulting from the ability of fish to detect glyphosate via olfaction. For imazapyr, SMM, and MSM the NDs were at concentrations low enough to rule out effects on all organisms other than aquatic plants, and the low concentration and (assumed) pulsed nature of any exposure should mitigate this potential. Integr Environ Assess Manag 2017;13:396-409. (C) 2016 SETAC

ABSTRACT Under the terms of the Clean Water Act, criteria for the protection of human health (Human Health Ambient Water Quality Criteria [HHWQC]) are traditionally derived using equations recommended by the US Environmental Protection Agency (USEPA) that include parameters for exposure assessment. To derive “adequately protective” HHWQC, USEPA proposes the use of default values for these parameters that are a combination of medians, means, and percentile estimates targeting the high end (90th percentile) of the general population. However, in practice, in nearly all cases, USEPA's recommended default assumptions represent upper percentiles. This article considers the adequacy of the exposure assessment component of USEPA‐recommended equations to yield criteria that are consistent with corresponding health protection targets established in USEPA recommendations or state policies, and concludes that conservative selections for exposure parameters can result in criteria that are substantially more protective than the health protection goals for HHWQC recommended by USEPA, due in large part to the compounding effect that occurs when multiple conservative factors are combined. This situation may be mitigated by thoughtful selection of exposure parameter values when using a deterministic approach, or by using a probabilistic approach based on data distributions for many of these parameters. Integr Environ Assess Manag 2015;11:298–305. © 2014 SETAC

Mercury (Hg) has been entering the environment from both natural and anthropogenic sources for millennia, and humans have been influencing its environmental transport and fate from well before the Industrial Revolution. Exposure to Hg (as neurotoxic monomethylmercury [MeHg]) occurs primarily through consumption of finfish, shellfish, and marine mammals, and regulatory limits for MeHg concentrations in fish tissue have steadily decreased as information on its health impacts has become available. These facts prompted us to consider 2 questions: 1) What might the MeHg levels in fish tissue have been in the pre‐Anthropocene, before significant human impacts on the environment? and 2) How would these pre‐Anthropocene levels have compared with current regulatory criteria for MeHg residues in fish tissue? We addressed the first question by estimating pre‐Anthropocene concentrations of MeHg in the tissues of prey and predatory fish with an integrated Hg speciation, transport, fate, and food web model (SERAFM), using estimated Hg concentrations in soil, sediment, and atmospheric deposition before the onset of significant human activity (i.e., ≤2000 BCE). Model results show MeHg residues in fish varying depending on the characteristics of the modeled water body, which suggests that Hg in fish tissue is best considered at the scale of individual watersheds or water bodies. We addressed the second question by comparing these model estimates with current regulatory criteria and found that MeHg residues in predatory (but not prey) fish could have approached or exceeded these criteria in some water bodies during the pre‐Anthropocene. This suggests that the possibility of naturally occurring levels of Hg in fish below which it is not possible to descend, regardless of where those levels stand with respect to current regulatory limits. Risk management decisions made under these circumstances have the potential to be ineffectual, frustrating, and costly for decision makers and stakeholders alike, suggesting the need for regulatory flexibility when addressing the issue of Hg in fish. Integr Environ Assess Manag 2014;10:299–308. © 2013 SETAC

Herbicides are an important tool for managing competitive vegetation in pine silviculture, and forestry best management practices (BMPs) were designed partly to minimize the movement of overland flow and dissolved herbicides into adjacent streams. We measured herbicide concentrations in streams before and after application when all modern forestry BMPs were applied to silvicultural operations. Imazapyr, hexazinone, and sulfometuron methyl were applied operationally to pine plantations covering 45 and 54

Nine small (2.2‐2.9 ha) and four large (70‐135 ha) watersheds in East Texas, USA, were instrumented to compare herbicide runoff under different silvicultural systems with best management practices (BMPs). Two treatments were evaluated: conventional, with clearcutting, aerial herbicide site preparation, and hand-applied banded herbaceous release; and intensive, in which subsoiling, aerial fertilization, and a 2nd-year aerial herbicide application were added. Herbicides were applied as operational tank mixes. The highest imazapyr concentration found in stream water was 39 μg L−1 during the first storm after application (23 days after treatment [DAT]) and in-stream concentrations during runoff events dropped to <1 μg L−1 in all streams by 150 DAT. The highest hexazinone concentration was 8 μg L−1 for the banded application and 35 μg L−1 for the broadcast application the following year and fell to <1 μg L−1 in all streams by 140 DAT. The highest sulfometuron methyl concentration found during a runoff event was 4 μg L−1 and fell to <1 μg L−1 in all streams by 80 DAT. Approximately 1‐2

Because many herbicides selectively control specific species or types of vegetation, they are often applied as mixtures to achieve better control over undesirable vegetation. When herbicides are applied in forest ecosystems, streams, ponds, and other bodies of water are typically protected by buffer zones in which no herbicide is applied. However, in some landscapes, small wetlands and streams are difficult to see and avoid, thus the potential acute toxicity of herbicide mixtures to aquatic organisms is of interest, yet it has not been well‐studied. We examined the acute toxicity of 23 different herbicide mixtures to Ceriodaphnia dubia and fathead minnows ( Pimephales promelas ) at environmentally relevant concentrations, and, where possible, characterized mixture interactions using Marking's Additive Index. Maximum exposure concentrations were equivalent to applying the maximum allowable rate for each component directly to the surface of a 6‐in. deep pond with no dissipation following application. Under the conditions of this study, herbicide formulations containing Accord Concentrate (glyphosate), Arsenal AC (imazapyr), Chopper (imazapyr), Escort (metsulfuron methyl), Oust XP (sulfometuron methyl), and Velpar L (hexazinone) were not associated with appreciable acute toxicity to fathead minnows or C. dubia when used alone or in mixtures with each other and various surfactants and adjuvants. Herbicide mixtures for which Additive Indexes could be calculated exhibited primarily antagonistic or simple additive toxicity. In the few cases where synergistic toxicity was observed, the degree of synergism was slight, never exceeding approximately twice the effect estimated based on additive toxicity. Based on the results of this study, neither acute toxicity nor enhanced acute aquatic toxicity due to synergistic mixture effects appears to be a significant concern for applications of the herbicide mixtures most commonly used in forestry. © 2011 Wiley Periodicals, Inc. Environ Toxicol 2012.