White Paper in Support of the Proposed Risk Assessment Process for Bees
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White Paper in Support of the Proposed Risk Assessment Process for Bees Submitted to the FIFRA Scientific Advisory Panel for Review and Comment September 11 – 14, 2012 Office of Chemical Safety and Pollution Prevention Office of Pesticide Programs Environmental Fate and Effects Division Washington, D. C. September 11, 2012 Environmental Assessment Directorate Pest Management Regulatory Agency Health Canada Ottawa, Canada K1A 0K9 California Department of Pesticide Regulation Sacramento, California Executive Summary Background Over the past 60 years, the number of managed honey bee (Apis mellifera) colonies in the U.S. has been in decline and recent reports have indicated that the numbers of insect pollinators are in decline both in North America and Europe. A number of factors have been associated with declines in honey bees in the North America including disease, pests, poor nutrition, loss of habitat, pesticides and bee management practices; however, none of these factors have been identified as the cause. Researchers have hypothesized that some of these factors may interact and result in losses which are attributed to winter kill and Colony Collapse Disorder. Although pesticides have not been implicated as the singular cause of insect pollinator declines in general or of declines in honey bees specifically, efforts have been directed at determining the extent to which pesticides may be affecting bees and ways to mitigate potential effects. Regulatory authorities in North America and elsewhere are developing improved procedures for evaluating the potential risks of pesticides to bees. While many pesticides are applied to foliar surfaces with the intention of affecting insects through contact, systemic pesticides can be applied to soil, seed or foliar surfaces and be transported to pollen and nectar where bees can be exposed through ingestion of residues. This paper considers exposures for foliar applied pesticides that may impact bees through contact and through the diet. This paper also addresses potential dietary exposures and effects of systemic pesticides on bees. Although a number of insects provide pollination services, this white paper focuses on the honey bee. The honey bee is a social organism that lives in hives which can contain in upwards of 50,000 bees that are primarily worker bees (females) further subdivided by castes, but all under the direction of a single queen. The individual bee cannot function independent of the hive for prolonged periods; therefore, the functional unit of the honey bee is the colony itself. Given that the hive is composed of thousands of bees, it has been likened to a “superorganism”. The attributes of the bee colony and its reliance on the queen represent challenges in assessing the potential risk of pesticides to bees since there can be complex routes of exposure and the colony can compensate for some losses given the redundancy that is built into the hive. Given the distance which bees can forage, spatial and temporal scales must be considered in evaluating potential exposure. The extent to which regulatory authorities have evaluated the potential risks of pesticides to bees has varied; however, there are efforts both internationally and domestically to improve the process. In North America, regulatory agencies have had relatively similar processes. Toxicity tests used to evaluate potential effects have been tiered and have first examined effects on individual bees under laboratory conditions while more refined testing is conducted using whole hives under field conditions. These processes are continuing to evolve to reflect the changing science. While EPA has evaluated the potential risks of pesticides to other taxa using a point estimate‐ based approach, it has historically only qualitatively described the potential hazard to bees. However, this paper describes a quantitative approach for developing risk quotients for bees. The proposed process is consistent with that used for other taxa in that it is both iterative and 2 tiered and takes into account both foliarly acting pesticides as well as those which are distributed systemically in plants. Increased levels of refinement focus on areas where specific risks may exist and are intended to be increasingly representative of actual use/exposure conditions. As with other taxa, the risk assessment ultimately depends on a collective understanding of available data which includes information from registrant‐submitted studies as well as information reported in the open literature and any data which may be available through incident reports. There are several challenges that exist when integrating the various exposure and effects data that can be used to assess potential effects of pesticides on honey bees and their colonies. For instance, different bees are expected to be exposed to pesticides at different magnitudes, depending upon their function in the colony. In addition, interpreting the impacts of mortality and sublethal effects on the ultimate survival of the colony is complicated by a lack of definitive understanding of the linkages between many of these endpoints. Colony‐level simulation models represent a useful tool that may be used to integrate exposure and effects data with the complexities of the social structure and biology of a honey bee colony. Consistent with the existing process, the white paper is organized similar to the proposed risk assessment process and is divided into three sections, i.e., problem formulation, analysis (exposure characterization and effects characterization) and risk characterization (estimation and discussion). Problem Formulation Problem formulation represents the initial phase of a risk assessment where management (protection) goals are defined and the subsequent assessment and measurement endpoints used in the assessment are articulated. This phase of a risk assessment also presents the conceptual models where the source of the stressor (pesticide use), routes of exposure, and effects (attribute changes) are also articulated. For bees, three protection goals are identified: pollination services, honey production and biodiversity. The primary assessment endpoints are colony survival, growth and reproduction and the proposed measurement endpoints include acute lethality to individual bees and measures of impaired survival, growth and reproduction of the colony itself. Several conceptual models are depicted to account for potential adverse effects from foliarly applied systemic and non‐systemic pesticides and from systemic pesticides applied to soil, seeds or tree trunks. Measures of effect are based primarily on honey bees because they are readily available, are relatively easy to work with under laboratory conditions and their husbandry needs are well documented both at the level of the individual bee as well as the colony. While the honey bee is the major focus of the process discussed in this paper, the honey bee is considered as a surrogate for other non‐Apis bees even though many of these other insect pollinators are not social and have life histories which are substantially different from that of the honey bee. Consistent with the process used for other terrestrial taxa (e.g., birds and mammals), screening‐ level estimated environmental concentrations used for evaluating exposure to honey bees are based on an existing tools (i.e., T‐REX model) as well as approaches for estimating exposure through ingestion of pollen and nectar containing residues of a systemic pesticide applied to soil or seeds that have not previously been used for regulatory purposes in North America. 3 Characterization of Exposure The proposed process for estimating exposure is consistent with that used for other taxa in that at a screening level (Tier I), exposure estimates are intended to be relatively conservative [high‐ end] while at higher tiers (Tiers II and III), exposure is based on measured values which are reflective of actual use conditions. While a number of routes of exposure are identified in the conceptual models depicted in the problem formulation, for pesticides that are applied via foliar spray, the primary routes of exposure are considered to be through contact and diet (i.e., consumption of contaminated pollen or nectar) and for systemic pesticides applied to soil and seeds, the primary route of exposure is through the diet. With these methods, dose‐based estimates of exposure through the diet are calculated by considering food consumption rates of larvae and adult worker bees and the estimated upper‐bound concentrations in pollen and nectar. The larval consumption rate is based on daily food consumption rates of worker larvae during the last two days of the uncapped period, while the adult worker bee food consumption rate is based on that of nectar foraging worker bees. Due to their relatively high food intake rates of worker larvae and nectar foraging bees, these two daily food consumption rates represent the portions of the larval and adult life stages that are expected to receive the greatest pesticide exposures when considering the entire life cycle of a worker bee. Different methods are presented to estimate pesticide concentrations in pollen and nectar for pesticide applications made via foliar spray, soil treatment, seed treatment and tree trunk applications. In screening‐level assessments contact exposure is estimated for pesticides applied via foliar spray. An upper‐bound residue value of chemicals on honey bees based on Koch and Weisser 1997 is proposed to represent contact exposures.