**1. Introduction**

Pesticides refer to a broad range of chemicals designed to control target organisms such as insects (insecticides), plants (herbicides), and other organisms (e.g. fungicides and algicides). While judicious use of pesticides can be beneficial, there is always a risk that non-target organisms will be affected. For some compounds, the widespread negative side-effects on non-target organisms outweigh the benefits of use. The classic examples of such compounds are DDT and other organochlorides. In the early 1960s, Rachel Carson published the book *Silent Spring*, which captured the public's attention on the widespread detrimental effects that organochlorides caused in the avian population such as embryotoxicity, eggshell thinning, and severe population declines [1, 2]. As a result of her work, DDT and other organochlorides were banned in the US beginning in the early 1970s with other developed countries following suit [1, 3].

Since the banning of organochlorides, new compounds have arisen to take their place such as neonicotinoids—the most widely used insecticides in the world with over 25% market share [4, 5]. Neonicotinoids have been in the spotlight in the pollinator community as they persist in the soil, have high water solubility, and have been associated with negative health implications on pollinators [5, 6]. The risk of these newer pesticides, including neonicotinoids, to bats are largely unknown, because required pesticide risk assessment schemes for birds and mammals have been deemed inadequate to assess the risk to bats [7].

This chapter will explore the how the natural life history of bats and their physiologic adaptations (e.g. echolocation, torpor and true, sustained flight [8]) increases their risk of oral, dermal, and inhalation exposure to pesticides. Understanding how Chiropteran ecology and physiology contribute to an increased risk of pesticide exposure is critical for several reasons. 1) Bats suffering from anthropogenic stressors such as environmental pollutants are at increased risk of immunosuppression—meaning an increase in the production and shedding of viruses [9, 10]. 2) Bats serve as important bioindicators for pesticide use and ecosystem health [11]—meaning the utilization of bats as bioindicators may be key to predicting emerging and re-emerging zoonotic diseases as recent zoonotic disease outbreaks have been closely interlinked to ecosystem health [12].

## **2. Worldwide pesticide use and registration of pesticides**

Worldwide, 3.5 million tons of pesticides were applied to farmland in 2020 [13, 14]. This is likely an underestimate, as the data was obtained from a selection of different databases—some of which are limited in their scope. For instance, one database used, the United States Geological Service (USGS) Pesticide National Synthesis Project, is a database that tracks agricultural pesticide use in the United States. In 2015, this database discontinued recording pesticides used in seed treatment applications [15]. The primary use of neonicotinoids are seed treatments [5], therefore neonicotinoids use is greatly underestimated in the United States, the second largest consumer of pesticides per the Food and Agriculture Organization of the United Nations (FAO) [16]. Additionally, many databases exclude non-agricultural pesticide products used by consumers (i.e. for home use and lawn/garden use), therefore true worldwide pesticide use is difficult to estimate.

Before a pesticide can be sold to consumers, each country undertakes a review process to validate the chemical is safe for nontarget species and efficacious. Typically, this process is allocated to governmental agencies (e.g., the Environmental Protection Agency (EPA) in the United States and the Europe Food Safety Authority (EFSA) in the European Union), or a government appointed board (e.g. The Pesticides and Toxic Chemicals Control Board in Saint Kitts and Nevis). While toxicology and ecotoxicological assessments vary by each country, the minimum requirements for most ecotoxicological studies must "(1) quantify the magnitude of acute mortality caused by the application, (2) determine the existence and extent of reproductive impairment in nontarget species from the application, and (3) determine the extent to which survival is influenced" [7, 17].

To fulfill these objectives, the study designs classically focus on obtaining the LD50, the lethal dose for 50% of a group of experimental animals; LC50, the lethal concentration in air or water that kills 50% of the experimental animals during a specific time period; and no-observed-effect-level (NOEL), the highest concentration of the substance at which no adverse effects are observed in the experimental animals. The experimental animals used to obtain the ecotoxicological data must be a species that is similar to those found in the desired application area. Typically

*Pesticide Exposure Risks to Chiropteran Species and the Impacts on Emerging Zoonotic Diseases DOI: http://dx.doi.org/10.5772/intechopen.100643*

rats (e.g. *Rattus norvegicus*) serve as the representative species for terrestrial mammals, the northern bobwhite (*Colinus virginianus*) or another quail species for an upland game bird, the mallard duck (*Anas platyrhynchos*) for waterfowl, and the house sparrow (*Passer domesticus*) or zebra finch (*Taeniopygia guttata*) for passerines [7, 17, 18]. Bats are classified as a terrestrial mammal for ecotoxicology testing purposes, and therefore are represented by rats, an r-selected species [19] without the physiological adaptations such as highly vascularized wings or echolocation.
