Environmental Toxicology and Chemistry, Vol. 34, No. 1, pp. 4–5, 2015 # 2014 SETAC Printed in the USA
Letter to the Editor
The authors’ reply:
emphasized for decades [7,8]. Data used to determine the effects of pesticide use in the tropics are almost entirely derived from perspectives of temperate developed regions. Ghose et al. [1] summarize the relative scarcity of ecotoxicological data for fungicides and nematicides widely used in tropical regions. Furthermore, typical ecotoxicological studies use laboratory conditions that mimic temperate rather than tropical temperatures. Ghose et al. [1] indicate several reasons why the lack of coverage is important to consider for the field of inquiry. In an extensive review, Kwok et al. [9] indicate that tropical aquatic species are often significantly more sensitive to contaminants than their temperate counterparts (italics added for emphasis). Furthermore, regardless of comparative species sensitivity, contaminants might be more toxic in tropical environments as a consequence of the intrinsic nature of tropical locations. Application of pesticides is often year round in tropical regions, and application rates may be much higher in tropical regions than temperate regions [10]. Climatic differences can alter chemical attributes such as exposure, uptake rates, fate, transport, and even how organisms are able to tolerate exposures [11]. Johnson et al. [12], using the same focal amphibian species as Ghose et al. [1], show that experimental toxicity tests done under tropical environmental conditions greatly increase toxicity estimates of chlorothalonil and endosulfan relative to “standard” laboratory conditions. Critically, many pesticides that have been banned over concerns about impacts on human or environmental health in North America and Europe are still widely used in the tropics and are not well regulated (including tridemorph, 1 of the compounds investigated by Ghose et al. [1]). Problematically, because most ecotoxicology research is conducted in wealthy countries and focuses on current-use pesticides of regional concern, those very pesticides that are considered to be too toxic for use by developed countries generally fall from the scrutiny of most ecotoxicological researchers. Attitudes such as those portrayed in the Weltje and Wheeler response to our report [2] may be part of why little research continues in tropical ecotoxicology.
Ghose et al. [1] reported an array of acute toxicity tests using aquatic amphibian larvae of a single species, combined with metaanalysis techniques, to illustrate that pesticides commonly used in Costa Rica are understudied relative to pesticides commonly used in the United States. In a response to our paper, Weltje and Wheeler [2] claim that the gaps we identified can be filled by the use of a fish surrogate model. They use our data combined with arguments from their previous work [3] and data from Kerby et al. [4] to argue that fish are suitable surrogates for all amphibian species (both temperate or tropical). They then conclude with the sweepingly broad claim that “no additional toxicity testing with (tropical) aquatic amphibians is needed.” This sophist approach to science makes for an intriguing argument, but on closer examination, the approach they suggest dissolves on many levels. Basic ecotoxicology follows many assumptions, and one must always consider these assumptions in regulatory decisions. The ideal conditions for toxicity testing cannot always be achieved as a consequence of limitations in funding (as Weltje and Wheeler point out [2]), and funding for basic toxicology testing is often very restricted in developing nations within the tropics. Weltje and Wheeler’s claim that ecotoxicology with amphibians is unnecessary runs counter to the fundamental principle of science as an iterative process in which knowledge is accumulated over time through subsequent observations and experiments [2]. Their argument is also dangerous because threats posed by pesticides and other contaminants may be overlooked even among well-studied ecotoxicological models and in wealthy countries where regulatory testing is required (e.g., Lundholm [5], Gill et al. [6]). The central premise of Ghose et al. [1] was that the use of data generated for temperate regions can be problematic for tropical species. Pesticides that are no longer approved for use in northern temperate regions are freely sold in developing countries where regulations on pesticide use are lax or absent. These lax regulations make toxicological studies in tropical regions critical for understanding impacts both to the environment and to human health and welfare. Weltje and Wheeler [2] do not address this fundamental point; rather, they propose the tangential idea that temperate fish species are equivalent to tropical amphibian species in toxicity testing. They overlook the research bias with regard to the types of pesticides that receive the most attention, and they fail to address sublethal effects on behavior and growth of organisms that would most likely differ between fish and amphibians.
FISH VERSUS AMPHIBIAN DATA
Amphibians evolved from fishes some 300 million years ago and were the first tetrapods to invade the terrestrial environment. Clearly, the ecological and physiological differences that are the product of different evolutionary paths are obvious to most biologists. Weltje and Wheeler simply compare toxicity data from fish with those from amphibians and conclude no significant difference. As a very illustration of the geographic biases we identified, Weltje and Wheeler support their conclusion by comparing data from our single tropical amphibian species with several species of temperate fish. Their comparison represents a limited approach to providing the “overwhelming support” they require for the ostentatious claim that further toxicity testing on tropical amphibians is unwarranted [2].Weltje and Wheeler [2] then attempt to reinforce their argument using a large dataset from a previous paper [3] that used findings obtained by Kerby et al. [4]. These 2 studies are
TEMPERATE VERSUS TROPICAL DATA
Tropical and temperate comparisons have captivated scientists for centuries. Tropical ecosystems are exceedingly complex and are in general understudied relative to temperate ecosystems. The gaps we highlighted in tropical ecotoxicology have been
Published online in Wiley Online Library (wileyonlinelibrary.com). DOI: 10.1002/etc.2779 4
Letter to the Editor
Environ Toxicol Chem 34, 2015
5
purported to provide support that “amphibians” are similarly sensitive to pesticides as “fish.” However, data from Kerby et al. [4] clearly show that a single amphibian species in the ECOTOX database can be several orders of magnitude more sensitive than a single fish species. Kerby et al. [4] did not conclude that fish were adequate surrogates for toxicity studies as Weltje et al. [3] argue. Instead, Kerby et al. [4] concluded that the use of a few species to represent entire classes of organisms was not warranted, and they explicitly advocate for a regional based approach to toxicity testing. Ghose et al. [1] recognize in their meta-analysis the substantial variation in species-specific toxicity to contaminants, and they use a statistical device, the geometric mean, to compensate for this variation that occurs over several orders of magnitude. Given the substantial variation among species in sensitivity to contaminants, the selective harvesting of large datasets apparently employed by Weltje and Wheeler [2] is dangerous because it ignores the speciesspecific responses characteristic of most studies that examine multiple taxa. Ultimately, the goal of regulation is not to protect on the basis of the average toxicity value, but rather to examine and protect the most sensitive species. For most endangered species, this is clearly a difficult task. Because approximately 40% of amphibians are at risk of extinction, and most amphibian species are found within the tropics, we believe that amphibians as a group warrant special scrutiny in ecotoxicological investigations. The phenomenal diversity of neotropical amphibians is unlikely to be captured by the study of the fathead minnow.
calls for data on tropical species (i.e., Lacher and Goldstein [7], Schiesari et al. [8], Kwok et al. [9]). Although identifying such obvious gaps is easy, the greater problem is how to fill these gaps in research with a vigorous research agenda. Developing nations in tropical regions seldom have sufficient research capacity or funding to address regional ecotoxicological concerns. Wealthy temperate countries that do have extensive research capacity, regulatory institutions, and research funding typically focus their resources on their own regional concerns. The question of whether gaps in tropical ecotoxicology exist is not up for debate; rather, the important question becomes how to promote a bold research agenda to fill these gaps.
TROPICAL AMPHIBIAN DIVERSITY
REFERENCES
Although one might find similarities between temperate amphibian species and freshwater fishes, one must consider the vast differences between the 2 groups of vertebrates. These differences span several levels of organization. Exposure routes must be considered; for instance, the red-eyed treefrog we tested deposits eggs on leaves, where herbicide or fungicide exposures might be considerably higher than for other species that deposit eggs in ponds and streams. Many tropical amphibians use small pools of water held by epiphytic plants in the rainforest as retreat sites, and these canopy pools can accumulate contaminants [13]. Many tropical amphibians never encounter water bodies but live their entire lives in terrestrial environments. These are all striking differences between “fish” and “amphibians.” Fundamental stress responses differ markedly between the 2 groups (cortisol vs corticosterone). Endocrine disruption has been exhibited in both fish and amphibians, but again via very different mechanisms. Using lethality data as regulatory controls overlooks important sublethal effects that are known to have important ecological implications (e.g., Kerby [14]); these implications are central to hypotheses linking pesticide-induced immunosuppression to disease emergence in amphibians. Beyond these substantial differences between “tropical amphibians” and “temperate fishes,” perhaps the most surprising gap is that we have little understanding of how tropical fishes compare with temperate fishes in their responses to chemicals used in developing countries. Before supporting the idea that “fish” can adequately represent “amphibians,” the most important task might be to determine whether fish from the temperate zone can adequately represent their tropical counterparts. Regulators may be forced to make decisions about the environmental safety of pesticides and other contaminants on the basis of limited data, but suggesting that continuing research on impacts of pesticides to tropical amphibians is unnecessary is dangerous and irresponsible. Ghose et al. [1] echo similar prior
1. Ghose SL, Donnelly MA, Kerby J, Whitfield SM. 2014. Acute toxicity tests and meta-analysis identify gaps in tropical ecotoxicology for amphibians. Environ Toxicol Chem 33:2114–2119. 2. Weltje L, Wheeler JR. 2015. Letter to the Editor. Environ Toxicol Chem 34:2–3 (this issue). 3. Weltje L, Simpson P, Gross M, Crane M, Wheeler JR. 2013. Comparative acute and chronic sensitivity of fish and amphibians: A critical review of data. Environ Toxicol Chem 32:984–994. 4. Kerby JL, Richards-Hrdlicka K, Storfer A, Skelly D. 2010. An examination of amphibian sensitivity to environmental contaminants: Are amphibians poor canaries? Ecol Lett 13:60–67. 5. Lundholm CD. 1997. DDE-induced eggshell thinning in birds. Comp Biochem Physiol C Pharmacol Toxicol Endocrinol 118:113–128. 6. Gill RJ, Ramos-Rodriguez O, Raine NE. 2012. Combined pesticide exposure severely affects individual- and colony-level traits in bees. Nature 491:105–108. 7. Lacher TE, Goldstein MI. 1997. Tropical ecotoxicology: Status and needs. Environ Toxicol Chem 16:100–111. 8. Schiesari L, Grillitsch B, Grillitsch H. 2007. Biogeographic biases in research and their consequences for linking amphibian declines to pollution. Conserv Biol 21:465–471. 9. Kwok KWH, Leung KMY, Lui GSG, Chu VKH, Lam PKS, Morrit D, Maltby L, Brock TCM, Van den Brink PJ, Warne M, Crane C. 2007. Comparison of tropical and temperate freshwater animal species’ acute sensitivities to chemicals: Implications for deriving safe extrapolation factors. Integr Environ Assess Manage 3:49–67. 10. de la Cruz E, Braco-Duran V, Ramirez F, Castillo LE. 2014. Environmental hazards associated with pesticide import into Costa Rica, 1977–2009. J Environ Biol 35:43–55. 11. Daam MA, Van den Brink PJ. 2010. Implications of differences between temperate and tropical freshwater ecosystems for the ecological risk assessment of pesticides. Ecotoxicology 19:24–37. 12. Johnson L, Welch B, Whitfield SM. 2013. Interactive effects of pesticide mixtures, predators, and temperature regimes on the toxicity of two pesticides to red-eyed tree frog larvae. Environ Toxicol Chem 32:2379– 2386. 13. Kaiser K. 2011. Preliminary study of pesticide drift into the Maya mountain protected areas of Belize. Bull Environ Contam Toxicol 86:56–59. 14. Kerby JL, Storfer A. 2011. Combined effects of atrazine and chlorpyrifos on susceptibility of the Tiger Salamander to Ambystoma tigrinum virus. Ecohealth 6:91–98.
Jacob L. Kerby University of South Dakota, USA Steven M. Whitfield Gonzaga University, USA Sonia L. Ghose California Academy of Sciences, USA Maureen A. Donnelly Florida International University, USA Acknowledgment—We dedicate this response to the memory of Margaret “Peggy” Mayfield.
Letter to the Editor
The authors’ reply:
emphasized for decades [7,8]. Data used to determine the effects of pesticide use in the tropics are almost entirely derived from perspectives of temperate developed regions. Ghose et al. [1] summarize the relative scarcity of ecotoxicological data for fungicides and nematicides widely used in tropical regions. Furthermore, typical ecotoxicological studies use laboratory conditions that mimic temperate rather than tropical temperatures. Ghose et al. [1] indicate several reasons why the lack of coverage is important to consider for the field of inquiry. In an extensive review, Kwok et al. [9] indicate that tropical aquatic species are often significantly more sensitive to contaminants than their temperate counterparts (italics added for emphasis). Furthermore, regardless of comparative species sensitivity, contaminants might be more toxic in tropical environments as a consequence of the intrinsic nature of tropical locations. Application of pesticides is often year round in tropical regions, and application rates may be much higher in tropical regions than temperate regions [10]. Climatic differences can alter chemical attributes such as exposure, uptake rates, fate, transport, and even how organisms are able to tolerate exposures [11]. Johnson et al. [12], using the same focal amphibian species as Ghose et al. [1], show that experimental toxicity tests done under tropical environmental conditions greatly increase toxicity estimates of chlorothalonil and endosulfan relative to “standard” laboratory conditions. Critically, many pesticides that have been banned over concerns about impacts on human or environmental health in North America and Europe are still widely used in the tropics and are not well regulated (including tridemorph, 1 of the compounds investigated by Ghose et al. [1]). Problematically, because most ecotoxicology research is conducted in wealthy countries and focuses on current-use pesticides of regional concern, those very pesticides that are considered to be too toxic for use by developed countries generally fall from the scrutiny of most ecotoxicological researchers. Attitudes such as those portrayed in the Weltje and Wheeler response to our report [2] may be part of why little research continues in tropical ecotoxicology.
Ghose et al. [1] reported an array of acute toxicity tests using aquatic amphibian larvae of a single species, combined with metaanalysis techniques, to illustrate that pesticides commonly used in Costa Rica are understudied relative to pesticides commonly used in the United States. In a response to our paper, Weltje and Wheeler [2] claim that the gaps we identified can be filled by the use of a fish surrogate model. They use our data combined with arguments from their previous work [3] and data from Kerby et al. [4] to argue that fish are suitable surrogates for all amphibian species (both temperate or tropical). They then conclude with the sweepingly broad claim that “no additional toxicity testing with (tropical) aquatic amphibians is needed.” This sophist approach to science makes for an intriguing argument, but on closer examination, the approach they suggest dissolves on many levels. Basic ecotoxicology follows many assumptions, and one must always consider these assumptions in regulatory decisions. The ideal conditions for toxicity testing cannot always be achieved as a consequence of limitations in funding (as Weltje and Wheeler point out [2]), and funding for basic toxicology testing is often very restricted in developing nations within the tropics. Weltje and Wheeler’s claim that ecotoxicology with amphibians is unnecessary runs counter to the fundamental principle of science as an iterative process in which knowledge is accumulated over time through subsequent observations and experiments [2]. Their argument is also dangerous because threats posed by pesticides and other contaminants may be overlooked even among well-studied ecotoxicological models and in wealthy countries where regulatory testing is required (e.g., Lundholm [5], Gill et al. [6]). The central premise of Ghose et al. [1] was that the use of data generated for temperate regions can be problematic for tropical species. Pesticides that are no longer approved for use in northern temperate regions are freely sold in developing countries where regulations on pesticide use are lax or absent. These lax regulations make toxicological studies in tropical regions critical for understanding impacts both to the environment and to human health and welfare. Weltje and Wheeler [2] do not address this fundamental point; rather, they propose the tangential idea that temperate fish species are equivalent to tropical amphibian species in toxicity testing. They overlook the research bias with regard to the types of pesticides that receive the most attention, and they fail to address sublethal effects on behavior and growth of organisms that would most likely differ between fish and amphibians.
FISH VERSUS AMPHIBIAN DATA
Amphibians evolved from fishes some 300 million years ago and were the first tetrapods to invade the terrestrial environment. Clearly, the ecological and physiological differences that are the product of different evolutionary paths are obvious to most biologists. Weltje and Wheeler simply compare toxicity data from fish with those from amphibians and conclude no significant difference. As a very illustration of the geographic biases we identified, Weltje and Wheeler support their conclusion by comparing data from our single tropical amphibian species with several species of temperate fish. Their comparison represents a limited approach to providing the “overwhelming support” they require for the ostentatious claim that further toxicity testing on tropical amphibians is unwarranted [2].Weltje and Wheeler [2] then attempt to reinforce their argument using a large dataset from a previous paper [3] that used findings obtained by Kerby et al. [4]. These 2 studies are
TEMPERATE VERSUS TROPICAL DATA
Tropical and temperate comparisons have captivated scientists for centuries. Tropical ecosystems are exceedingly complex and are in general understudied relative to temperate ecosystems. The gaps we highlighted in tropical ecotoxicology have been
Published online in Wiley Online Library (wileyonlinelibrary.com). DOI: 10.1002/etc.2779 4
Letter to the Editor
Environ Toxicol Chem 34, 2015
5
purported to provide support that “amphibians” are similarly sensitive to pesticides as “fish.” However, data from Kerby et al. [4] clearly show that a single amphibian species in the ECOTOX database can be several orders of magnitude more sensitive than a single fish species. Kerby et al. [4] did not conclude that fish were adequate surrogates for toxicity studies as Weltje et al. [3] argue. Instead, Kerby et al. [4] concluded that the use of a few species to represent entire classes of organisms was not warranted, and they explicitly advocate for a regional based approach to toxicity testing. Ghose et al. [1] recognize in their meta-analysis the substantial variation in species-specific toxicity to contaminants, and they use a statistical device, the geometric mean, to compensate for this variation that occurs over several orders of magnitude. Given the substantial variation among species in sensitivity to contaminants, the selective harvesting of large datasets apparently employed by Weltje and Wheeler [2] is dangerous because it ignores the speciesspecific responses characteristic of most studies that examine multiple taxa. Ultimately, the goal of regulation is not to protect on the basis of the average toxicity value, but rather to examine and protect the most sensitive species. For most endangered species, this is clearly a difficult task. Because approximately 40% of amphibians are at risk of extinction, and most amphibian species are found within the tropics, we believe that amphibians as a group warrant special scrutiny in ecotoxicological investigations. The phenomenal diversity of neotropical amphibians is unlikely to be captured by the study of the fathead minnow.
calls for data on tropical species (i.e., Lacher and Goldstein [7], Schiesari et al. [8], Kwok et al. [9]). Although identifying such obvious gaps is easy, the greater problem is how to fill these gaps in research with a vigorous research agenda. Developing nations in tropical regions seldom have sufficient research capacity or funding to address regional ecotoxicological concerns. Wealthy temperate countries that do have extensive research capacity, regulatory institutions, and research funding typically focus their resources on their own regional concerns. The question of whether gaps in tropical ecotoxicology exist is not up for debate; rather, the important question becomes how to promote a bold research agenda to fill these gaps.
TROPICAL AMPHIBIAN DIVERSITY
REFERENCES
Although one might find similarities between temperate amphibian species and freshwater fishes, one must consider the vast differences between the 2 groups of vertebrates. These differences span several levels of organization. Exposure routes must be considered; for instance, the red-eyed treefrog we tested deposits eggs on leaves, where herbicide or fungicide exposures might be considerably higher than for other species that deposit eggs in ponds and streams. Many tropical amphibians use small pools of water held by epiphytic plants in the rainforest as retreat sites, and these canopy pools can accumulate contaminants [13]. Many tropical amphibians never encounter water bodies but live their entire lives in terrestrial environments. These are all striking differences between “fish” and “amphibians.” Fundamental stress responses differ markedly between the 2 groups (cortisol vs corticosterone). Endocrine disruption has been exhibited in both fish and amphibians, but again via very different mechanisms. Using lethality data as regulatory controls overlooks important sublethal effects that are known to have important ecological implications (e.g., Kerby [14]); these implications are central to hypotheses linking pesticide-induced immunosuppression to disease emergence in amphibians. Beyond these substantial differences between “tropical amphibians” and “temperate fishes,” perhaps the most surprising gap is that we have little understanding of how tropical fishes compare with temperate fishes in their responses to chemicals used in developing countries. Before supporting the idea that “fish” can adequately represent “amphibians,” the most important task might be to determine whether fish from the temperate zone can adequately represent their tropical counterparts. Regulators may be forced to make decisions about the environmental safety of pesticides and other contaminants on the basis of limited data, but suggesting that continuing research on impacts of pesticides to tropical amphibians is unnecessary is dangerous and irresponsible. Ghose et al. [1] echo similar prior
1. Ghose SL, Donnelly MA, Kerby J, Whitfield SM. 2014. Acute toxicity tests and meta-analysis identify gaps in tropical ecotoxicology for amphibians. Environ Toxicol Chem 33:2114–2119. 2. Weltje L, Wheeler JR. 2015. Letter to the Editor. Environ Toxicol Chem 34:2–3 (this issue). 3. Weltje L, Simpson P, Gross M, Crane M, Wheeler JR. 2013. Comparative acute and chronic sensitivity of fish and amphibians: A critical review of data. Environ Toxicol Chem 32:984–994. 4. Kerby JL, Richards-Hrdlicka K, Storfer A, Skelly D. 2010. An examination of amphibian sensitivity to environmental contaminants: Are amphibians poor canaries? Ecol Lett 13:60–67. 5. Lundholm CD. 1997. DDE-induced eggshell thinning in birds. Comp Biochem Physiol C Pharmacol Toxicol Endocrinol 118:113–128. 6. Gill RJ, Ramos-Rodriguez O, Raine NE. 2012. Combined pesticide exposure severely affects individual- and colony-level traits in bees. Nature 491:105–108. 7. Lacher TE, Goldstein MI. 1997. Tropical ecotoxicology: Status and needs. Environ Toxicol Chem 16:100–111. 8. Schiesari L, Grillitsch B, Grillitsch H. 2007. Biogeographic biases in research and their consequences for linking amphibian declines to pollution. Conserv Biol 21:465–471. 9. Kwok KWH, Leung KMY, Lui GSG, Chu VKH, Lam PKS, Morrit D, Maltby L, Brock TCM, Van den Brink PJ, Warne M, Crane C. 2007. Comparison of tropical and temperate freshwater animal species’ acute sensitivities to chemicals: Implications for deriving safe extrapolation factors. Integr Environ Assess Manage 3:49–67. 10. de la Cruz E, Braco-Duran V, Ramirez F, Castillo LE. 2014. Environmental hazards associated with pesticide import into Costa Rica, 1977–2009. J Environ Biol 35:43–55. 11. Daam MA, Van den Brink PJ. 2010. Implications of differences between temperate and tropical freshwater ecosystems for the ecological risk assessment of pesticides. Ecotoxicology 19:24–37. 12. Johnson L, Welch B, Whitfield SM. 2013. Interactive effects of pesticide mixtures, predators, and temperature regimes on the toxicity of two pesticides to red-eyed tree frog larvae. Environ Toxicol Chem 32:2379– 2386. 13. Kaiser K. 2011. Preliminary study of pesticide drift into the Maya mountain protected areas of Belize. Bull Environ Contam Toxicol 86:56–59. 14. Kerby JL, Storfer A. 2011. Combined effects of atrazine and chlorpyrifos on susceptibility of the Tiger Salamander to Ambystoma tigrinum virus. Ecohealth 6:91–98.
Jacob L. Kerby University of South Dakota, USA Steven M. Whitfield Gonzaga University, USA Sonia L. Ghose California Academy of Sciences, USA Maureen A. Donnelly Florida International University, USA Acknowledgment—We dedicate this response to the memory of Margaret “Peggy” Mayfield.
