**2.6 Effects on birds**

Pesticides have had some of their most striking effects on birds, particularly those in the higher trophic levels of food chains, such as bald eagles, hawks, and owls. These birds are often rare, endangered, and susceptible to pesticide residues such as those occurring from the bioconcentration of organochlorine insecticides through terrestrial food chains. Pesticides may kill grain- and plant-feeding birds, and the elimination of many rare species of ducks and geese has been reported. Populations of insect-eating birds such as partridges, grouse, and pheasants have decreased due to the loss of their insect food in agricultural fields through the use of insecticides. The loss of even a few individuals from rare, endangered or threatened species pushes the entire species close to extinction. Some pertinent examples associated with birds' kills as a result of pesticides include the insecticides diazinon and carbofuran which are well document as causing bird kills in many parts of the world (Kegley *et al*, 1999). Organochlorine insecticides such as DDT are also well

Ecological Effects of Pesticides 137

Atrazine being one of the world`s most used pesticide has recently reported by laboratory studies to have a effect on changing male frogs (African clawed frog; *Xenopus laevis*). Adult frogs exposed to atrazine turn female one in ten (10%). These male frogs are missing

Fig. 2.6. Spraying an aquatic herbicide

**2.8 Effects on frogs and other aquatic amphibians** 

Fig. 2.7 Kihansi spray toads from Kihansi Gorge in Tanzania

documented to have continued impairing avian reproduction even after years of banned use. Most bird kills go undocumented, with reported kills representing only a small fraction of actual bird mortality due to pesticides.

Birds exposed to sublethal doses of pesticides are also afflicted with chronic symptoms that affect their behaviour, reproduction, and nervous system. Weight loss, increased susceptibility to predation, decreased disease resistance, lack of interest in mating and defending territory, and abandoning of nestlings have been observed as side effects of pesticides exposure.

Fig. 2.5 A bird that died as a result of pesticides use (U.S. EPA)

#### **2.7 Effects on fish and other aquatic organisms**

A major environmental impact has been the widespread mortality of fish and marine invertebrates due to the contamination of aquatic systems by pesticides. This has resulted from the agricultural contamination of waterways through fallout, drainage, or runoff erosion, and from the discharge of industrial effluents containing pesticides into waterways. Historically, most of the fish in Europe's Rhine River were killed by the discharge of pesticides, and at one time fish populations in the Great Lakes in USA became very low due to pesticide contamination. Additionally, many of the organisms that provide food for fish are extremely susceptible to pesticides, so the indirect effects of pesticides on the fish food supply may have an even greater effect on fish populations. Some pesticides, such as pyrethroid insecticides, are extremely toxic to most aquatic organisms. It is evident that pesticides cause major losses in global fish production. Furthermore, recent laboratory studies of endosulfan and fenitrothion in the tilapia species from Lake Victoria in Tanzania indicated a high capacity of the species to absorb the two pesticides from water with rapid distribution in the organs each with a bioaccumulation factor of 33 and 346 L/kg fresh weight respectively (Henry, 2003).

Multiple pesticides contamination are very common in water and sediments, frequently at concentrations exceeding the lethal limits for many species of zooplankton, small species of animals eaten by fish. Because of the significant high water solubility of the insecticides diazinon and chlorpyrifos and the herbicides simazine, diron, and EPTC are found most commonly in water bodies and have been associated with fish kills and decline in zooplankton population in aquatic environment.

documented to have continued impairing avian reproduction even after years of banned use. Most bird kills go undocumented, with reported kills representing only a small fraction

Birds exposed to sublethal doses of pesticides are also afflicted with chronic symptoms that affect their behaviour, reproduction, and nervous system. Weight loss, increased susceptibility to predation, decreased disease resistance, lack of interest in mating and defending territory, and abandoning of nestlings have been observed as side effects of

A major environmental impact has been the widespread mortality of fish and marine invertebrates due to the contamination of aquatic systems by pesticides. This has resulted from the agricultural contamination of waterways through fallout, drainage, or runoff erosion, and from the discharge of industrial effluents containing pesticides into waterways. Historically, most of the fish in Europe's Rhine River were killed by the discharge of pesticides, and at one time fish populations in the Great Lakes in USA became very low due to pesticide contamination. Additionally, many of the organisms that provide food for fish are extremely susceptible to pesticides, so the indirect effects of pesticides on the fish food supply may have an even greater effect on fish populations. Some pesticides, such as pyrethroid insecticides, are extremely toxic to most aquatic organisms. It is evident that pesticides cause major losses in global fish production. Furthermore, recent laboratory studies of endosulfan and fenitrothion in the tilapia species from Lake Victoria in Tanzania indicated a high capacity of the species to absorb the two pesticides from water with rapid distribution in the organs each with a bioaccumulation factor of 33 and 346 L/kg fresh

Multiple pesticides contamination are very common in water and sediments, frequently at concentrations exceeding the lethal limits for many species of zooplankton, small species of animals eaten by fish. Because of the significant high water solubility of the insecticides diazinon and chlorpyrifos and the herbicides simazine, diron, and EPTC are found most commonly in water bodies and have been associated with fish kills and decline in

of actual bird mortality due to pesticides.

Fig. 2.5 A bird that died as a result of pesticides use (U.S. EPA)

**2.7 Effects on fish and other aquatic organisms** 

weight respectively (Henry, 2003).

zooplankton population in aquatic environment.

pesticides exposure.

Fig. 2.6. Spraying an aquatic herbicide

#### **2.8 Effects on frogs and other aquatic amphibians**

Atrazine being one of the world`s most used pesticide has recently reported by laboratory studies to have a effect on changing male frogs (African clawed frog; *Xenopus laevis*). Adult frogs exposed to atrazine turn female one in ten (10%). These male frogs are missing

Fig. 2.7 Kihansi spray toads from Kihansi Gorge in Tanzania

Ecological Effects of Pesticides 139

Non-target organisms, organisms that the pesticides are not intended to be killed, can be severely affected by the use of pesticides. In some cases, where a pest insect has some controls from a beneficial predator or parasite, an insecticide application can kill both pest and beneficial populations. A study comparing biological pest control and use of pyrethroid insecticide for diamondback moths, a major cabbage family insect pest, showed that, the insecticide application created a rebounded pest population due to loss of insect predators, whereas the biological control did not show the same effect (Muckenfuss, *et al* 1990). Likewise, pesticides sprayed in an effort to control adult mosquitoes, may temporarily depress mosquito populations, however they may result in a larger population in the long run by damaging the natural controlling factors. This phenomenon, wherein the population of a pest species rebounds to equal or greater numbers than it had before pesticide use, is called pest resurgence and can be linked to elimination of predators and other natural

The loss of predator species can also lead to a related phenomenon called secondary pest outbreaks, an increase in problems from species which were not originally very damaging pests due to loss of their predators or parasites (Daly, *et at*, 1998). An estimated one-third of the 300 most damaging insects in the US were originally secondary pests and only became a major problem after the use of pesticides (Miller, 2004). In both pest resurgence and secondary pest outbreaks, the natural enemies have been found to be more susceptible to the pesticides than the pests themselves, in some cases causing the pest population to be

Pesticides can enter the human body through inhalation of aerosols, dust and vapor that contain pesticides; through oral exposure by consuming contaminated food and water; and through dermal exposure by direct contact of pesticides with skin (Sacramento, 2008). Pesticides are sprayed onto food, especially fruits and vegetables, they secrete into soils and groundwater which can end up in drinking water, and pesticide spray can drift and pollute

The effects of pesticides on human health are more harmful based on the toxicity of the chemical and the length and magnitude of exposure (Lorenz, 2009). Farm workers and their families experience the greatest exposure to agricultural pesticides through direct contact with the chemicals. But every human contains a percentage of pesticides found in fat samples in their body. Children are most susceptible and sensitive to pesticides due to their small size and underdevelopment. The chemicals can bioaccumulate in the body over time. Exposure to pesticides can range from mild skin irritation to birth defects, tumors, genetic changes, blood

Pests may evolve to become resistant to pesticides as a result of continued use of pesticides in a particular environment. Many pests will initially be very susceptible to pesticides, but some with slight variations in their genetic makeup they become resistant and therefore survive to reproduce. Through natural selection, the pests may eventually become very resistant to the pesticide. Pest resistance to a pesticide is commonly managed through pesticide rotation, which involves alternating among pesticide classes with different modes of action to delay the

and nerve disorders, endocrine disruption, and even coma or death (Miller, 2004).

**2.10 Pesticides cause pest rebound and secondary pest outbreaks** 

enemies of the pest (Daly, *et at*, 1998).

higher than it was before the use of pesticide.

**2.12 Pesticides may cause pest resistance** 

**2.11 Effects on human beings** 

the air.

testesterone and all things controlled by testesterone including sperm production. So their fertility is as low as 10 percent when treated in isolation, but when treated with normal males, they stand a zero chance of reproducing. Although 10 percent of these mutant females can successful mate with male frogs, their offspring are all male because they are genetically male frogs. The ultmate effect of this is that the sex ratios of frogs is badly skewed and this is very dangerous for the survival of that species (Hayes *et al*, 2010).Kihansi spray toads is one among the world`s rarest amphibian species that was close to extinction from their natural environment in Tanzania. The species was first discovered in 1996 during an environment impact study for a large new hydroelectic dam in Udzungwa mountains in Southern Tanzania. The toads lived exclusively in a five acre zone under spray of a waterfall from Udzungwa mountains, hence the name Kihansi spray toads. Among other reasons that contributed to the decline is the use of pesticides in the environment. To rescue this rare species of toads, a colony of them was taken to Bronx zoo and Toledo zoo in USA where they were reared and bread in laboratories for 10 years.

#### **2.9 Pesticides disrupt the natural balance between pest and predator insects**

Broad spectrum pesticides such as organochlorine, organophosphorus and carbamate insecticides destroy both pest and beneficial organisms indiscriminately, thus upsetting the natural balance between pests and predator insects. Beneficial organisms serve many valuable functions in an agricultural ecosystem including pollination, soil aeration, nutrient cycling, and natural pest control through pest-predator relationship. Application of insecticides indiscriminately kills both pests and beneficial organisms. Pest populations often recover rapidly because of their lager numbers and ability to develop resistance, but beneficial organisms do not, resulting in a resurgence of the target pest as well as secondary pests that reproduce rapidly without natural predator to check down their numbers. This prompts an escalation in the use of more pesticides by the farmers in an attempt to control them and boost their harvest.

Fig. 2.8 Aerial spraying of pesticides onto the crops using an aircraft

testesterone and all things controlled by testesterone including sperm production. So their fertility is as low as 10 percent when treated in isolation, but when treated with normal males, they stand a zero chance of reproducing. Although 10 percent of these mutant females can successful mate with male frogs, their offspring are all male because they are genetically male frogs. The ultmate effect of this is that the sex ratios of frogs is badly skewed and this is very dangerous for the survival of that species (Hayes *et al*, 2010).Kihansi spray toads is one among the world`s rarest amphibian species that was close to extinction from their natural environment in Tanzania. The species was first discovered in 1996 during an environment impact study for a large new hydroelectic dam in Udzungwa mountains in Southern Tanzania. The toads lived exclusively in a five acre zone under spray of a waterfall from Udzungwa mountains, hence the name Kihansi spray toads. Among other reasons that contributed to the decline is the use of pesticides in the environment. To rescue this rare species of toads, a colony of them was taken to Bronx zoo and Toledo zoo in USA where

**2.9 Pesticides disrupt the natural balance between pest and predator insects** 

Fig. 2.8 Aerial spraying of pesticides onto the crops using an aircraft

Broad spectrum pesticides such as organochlorine, organophosphorus and carbamate insecticides destroy both pest and beneficial organisms indiscriminately, thus upsetting the natural balance between pests and predator insects. Beneficial organisms serve many valuable functions in an agricultural ecosystem including pollination, soil aeration, nutrient cycling, and natural pest control through pest-predator relationship. Application of insecticides indiscriminately kills both pests and beneficial organisms. Pest populations often recover rapidly because of their lager numbers and ability to develop resistance, but beneficial organisms do not, resulting in a resurgence of the target pest as well as secondary pests that reproduce rapidly without natural predator to check down their numbers. This prompts an escalation in the use of more pesticides by the farmers in an attempt to control

they were reared and bread in laboratories for 10 years.

them and boost their harvest.

#### **2.10 Pesticides cause pest rebound and secondary pest outbreaks**

Non-target organisms, organisms that the pesticides are not intended to be killed, can be severely affected by the use of pesticides. In some cases, where a pest insect has some controls from a beneficial predator or parasite, an insecticide application can kill both pest and beneficial populations. A study comparing biological pest control and use of pyrethroid insecticide for diamondback moths, a major cabbage family insect pest, showed that, the insecticide application created a rebounded pest population due to loss of insect predators, whereas the biological control did not show the same effect (Muckenfuss, *et al* 1990). Likewise, pesticides sprayed in an effort to control adult mosquitoes, may temporarily depress mosquito populations, however they may result in a larger population in the long run by damaging the natural controlling factors. This phenomenon, wherein the population of a pest species rebounds to equal or greater numbers than it had before pesticide use, is called pest resurgence and can be linked to elimination of predators and other natural enemies of the pest (Daly, *et at*, 1998).

The loss of predator species can also lead to a related phenomenon called secondary pest outbreaks, an increase in problems from species which were not originally very damaging pests due to loss of their predators or parasites (Daly, *et at*, 1998). An estimated one-third of the 300 most damaging insects in the US were originally secondary pests and only became a major problem after the use of pesticides (Miller, 2004). In both pest resurgence and secondary pest outbreaks, the natural enemies have been found to be more susceptible to the pesticides than the pests themselves, in some cases causing the pest population to be higher than it was before the use of pesticide.

#### **2.11 Effects on human beings**

Pesticides can enter the human body through inhalation of aerosols, dust and vapor that contain pesticides; through oral exposure by consuming contaminated food and water; and through dermal exposure by direct contact of pesticides with skin (Sacramento, 2008). Pesticides are sprayed onto food, especially fruits and vegetables, they secrete into soils and groundwater which can end up in drinking water, and pesticide spray can drift and pollute the air.

The effects of pesticides on human health are more harmful based on the toxicity of the chemical and the length and magnitude of exposure (Lorenz, 2009). Farm workers and their families experience the greatest exposure to agricultural pesticides through direct contact with the chemicals. But every human contains a percentage of pesticides found in fat samples in their body. Children are most susceptible and sensitive to pesticides due to their small size and underdevelopment. The chemicals can bioaccumulate in the body over time. Exposure to pesticides can range from mild skin irritation to birth defects, tumors, genetic changes, blood and nerve disorders, endocrine disruption, and even coma or death (Miller, 2004).

#### **2.12 Pesticides may cause pest resistance**

Pests may evolve to become resistant to pesticides as a result of continued use of pesticides in a particular environment. Many pests will initially be very susceptible to pesticides, but some with slight variations in their genetic makeup they become resistant and therefore survive to reproduce. Through natural selection, the pests may eventually become very resistant to the pesticide. Pest resistance to a pesticide is commonly managed through pesticide rotation, which involves alternating among pesticide classes with different modes of action to delay the

Ecological Effects of Pesticides 141

air, we are all taking part in an experiment in pesticide exposure on a global scale, but without the benefit of an exposed control group for comparison. For that matter we are likely not be able to quantify the exact risk of these exposures. Because we cannot know for certain the consequences of the expanding pesticides use, the rational and most protective course of action is to take a precaution approach phasing out the use of the most dangerous pesticides, reducing our reliance on toxic chemicals for pest control and promoting

The adverse effects of pesticides on humans and wildlife have resulted in research into ways of reducing pesticide use. The most important of these is the concept of integrated pest management (IPM), first introduced in 1959. This combines minimal use of the least harmful pesticides, integrated with biological and cultural methods of minimizing pest losses. It is linked with using pesticides only when threshold levels of pest attacks have been identified. There is also a move toward sustainable agriculture which aims to minimize use of

There has been a growing concern recently on the promotion of organic farming which emphasize on techniques such as crop rotation, green manure, compost and biological methods of pest control to maintain soil productivity. Organic farming strictly excludes the use of manufactured fertilizers, pesticides, plant growth regulators, livestock antibiotics, food additives, and genetically modified organisms. Organic foods resulting from organic farming are deemed free from pesticides and hence providing an alternative source of quality and safe food in the future. By promoting the use of organic foods means will push the farmers to opt for organic farming. Market forces are a powerful incentive to encourage

Pesticides manufacturers should conduct long-term studies on ecosystem-wide impacts to demonstrate that a pesticide has no adverse effects before allowing it to be registered for use in the environment. The fact that present regulations view a pesticide as innocent until proved guilty is detrimental to the environment health. It is critical to know more about the long-term ecological effects of a pesticide before it is released to the environment. Using a combination of prior gained field experience with the existing pesticides and applying fundamental chemodynamic principles to newly developed compounds, we can now predict with some degree of accuracy the fate of new chemicals before they are even used in

Johnson, M. T.; Strinchcombe, J. R. (2007). "An emerging synthesis between community ecology and evolutionary biology". *Trends in Ecology and Evolution* 22 (5): 250–7 Harrison, S. A. (1990). The Fate of Pesticides in the Environment, Agrochemical Fact Sheet #

Helweg, C. *et al* (2003). Fate of pesticides in surface waters, Laboratory and Field

Kegley, S. *et al* (1999). Disrupting the Balance, Ecological Impacts of Pesticides in California,

Hackenberg D (2007). "Letter from David Hackenberg to American growers. Plattform

Experiments; Ministry of Environment, Danish Environmental Protection Agency,.

ecologically based pest management.

famers to go organic.

the environment.

**4. References** 

8, Penn, USA

California, USA

Imkerinnen Austria.

Pesticides Research No. 68.

pesticides and fertilizers based on a systems approach.

onset of or mitigate existing pest resistance. Tank mixing pesticides is the combination of two or more pesticides with different modes of action in order to improve individual pesticide application results and delay the onset of or mitigate existing pest resistance.

Fig. 2.9 Impacts of pesticides on human health
