**2. Necessity of remediation of soil and groundwater polluted by pesticides**

#### **2.1. Harmful influences of pesticides on living organisms**

Typical pesticides employed in the agriculture sector are shown in Figure 1. Until the 1980s, organochlorine insecticides, such as DDT and BHC, were the most commonly used agents. However, Rachel L. Carson warned in her book "Silent Spring," which was published in 1962, that these insecticides were hard to degrade and subject to accumulation in the environment. In fact, many deformed birds and fish that had accumulated the organochlorine compounds were found. Based on this book and the findings of numerous other scientists, the production and utilization of DDT is now forbidden in many countries. Moreover, the discontinuation of persistent organic pollutants (POPs) such as DDT and BHC was decided to be a worldwide goal at the Stockholm Convention on Persistent Organic Pollutants in 2001. As a result, DDT cannot be used except for eliminating mosquitoes carrying malaria.

Following the banning of POPs, organophosphorous insecticides, such as parathion, dichlor‐ vos, penitrothione and diazinon, were gradually applied to patties and fields instead of DDT and BHC. The persistence of organophosphorous compounds is much lower than that of DDT or BHC. These compounds, however, strongly inhibit the activity of acethylcholine esterase in nerve cells, and some of them showed strong toxicity to humans [3]. The use of many orga‐ nophosphorous compounds was prohibited by the European Union (EU) in the 2000s, but they are still used in other countries. The derivatives of pyrethroid, such as chrysanthemic acid and pyrethrolone, and the derivatives of nicotine, such as imidacloprid, were similarly developed to decrease the toxicity of these herbicides. Imidacloprid is currently speculated to be the cause of colony collapse disorder, but remains widely use all over the world.

Another compound, 2,4-dichlorophenoxyacetic acid (2,4-D), was first developed in 1944 as a weed killer for treating wheat and corn fields. The compound kills dicotyledons, but functions as a phytohormone for monocotyledons. It is still used today. Triazine herbicides, such as atrazine and simazine, were developed as weed killers in the 1970s. These compounds kill weeds after absorption from the leaves and roots. They were used in Europe and the United States with great success, but atrazine was subsequently found to act as an endocrine disruptor [4,5]. According to Hayes *et al*. [4], when 40 male frogs (*Xenopus laevis*) were exposed to water containing 2.5 ppm of atrazine for three years, 30 frogs became infertile and four frogs became females. The four female frogs could be fertilized by a male frog. These results strongly suggested that atrazine was harmful. The EU decided to prohibit the use of atrazine after noting that concentrations often exceeded the upper limit in groundwater. The US Environmental Protection Agency (EPA) set the upper limit of atrazine as 3 ppm in the drinking water, which was much higher than that in the EU. The EPA does not currently prohibit the utilization of atrazine, because the proof of adverse effects was not considered to be reliable. Therefore, atrazine is still used in the United States. Some specialists also warn that the sharp decrease of frogs in all over the world might be related to the excess use of triazine herbicides.

**Figure 1.** Pesticides commonly used for agriculture.

costs cannot be applied for this pollution. Therefore, the development of a new bioremediation

In this chapter, the author proposed a novel bioremediation method called "Bioremediation with the self-immobilized system (BSIS)". Using this method, degrading microorganism can be self-immobilized by the help of *Bacillus subtilis*, and the immobilized cells rapidly degrade the pollutant in the shallow layer of the soil. The equipment and running cost associated with BSIS are low, and therefore, I think that this method is a superior method for remediating soil

**2. Necessity of remediation of soil and groundwater polluted by pesticides**

Typical pesticides employed in the agriculture sector are shown in Figure 1. Until the 1980s, organochlorine insecticides, such as DDT and BHC, were the most commonly used agents. However, Rachel L. Carson warned in her book "Silent Spring," which was published in 1962, that these insecticides were hard to degrade and subject to accumulation in the environment. In fact, many deformed birds and fish that had accumulated the organochlorine compounds were found. Based on this book and the findings of numerous other scientists, the production and utilization of DDT is now forbidden in many countries. Moreover, the discontinuation of persistent organic pollutants (POPs) such as DDT and BHC was decided to be a worldwide goal at the Stockholm Convention on Persistent Organic Pollutants in 2001. As a result, DDT

Following the banning of POPs, organophosphorous insecticides, such as parathion, dichlor‐ vos, penitrothione and diazinon, were gradually applied to patties and fields instead of DDT and BHC. The persistence of organophosphorous compounds is much lower than that of DDT or BHC. These compounds, however, strongly inhibit the activity of acethylcholine esterase in nerve cells, and some of them showed strong toxicity to humans [3]. The use of many orga‐ nophosphorous compounds was prohibited by the European Union (EU) in the 2000s, but they are still used in other countries. The derivatives of pyrethroid, such as chrysanthemic acid and pyrethrolone, and the derivatives of nicotine, such as imidacloprid, were similarly developed to decrease the toxicity of these herbicides. Imidacloprid is currently speculated to be the cause

Another compound, 2,4-dichlorophenoxyacetic acid (2,4-D), was first developed in 1944 as a weed killer for treating wheat and corn fields. The compound kills dicotyledons, but functions as a phytohormone for monocotyledons. It is still used today. Triazine herbicides, such as atrazine and simazine, were developed as weed killers in the 1970s. These compounds kill weeds after absorption from the leaves and roots. They were used in Europe and the United States with great success, but atrazine was subsequently found to act as an endocrine disruptor [4,5]. According to Hayes *et al*. [4], when 40 male frogs (*Xenopus laevis*) were exposed to water containing 2.5 ppm of atrazine for three years, 30 frogs became infertile and four frogs became

method, which is applicable to huge areas and is low cost, has been desired.

**2.1. Harmful influences of pesticides on living organisms**

cannot be used except for eliminating mosquitoes carrying malaria.

of colony collapse disorder, but remains widely use all over the world.

polluted by pesticides.

286 Applied Bioremediation - Active and Passive Approaches

In the 1980s, Roundup was developed by Monsant Company. Glyphosate-isopropyl ammo‐ nium is a main component of the herbicide. It inhibits the synthesis of an amino acid, and works against all kinds of plants. The company also developed genetically modified organisms (GMO) which were resistant to Roundup. Based on these successes, Roundup is widely used to grow GMO in the United States. However, excess utilization of the non-selective herbicides (2, 4-D and Roundup) causes a decrease in soil insects and bacteria, which supply the nitrogen, carbon and phosphate sources to plants.

As described above, the use of many harmful herbicides has been prohibited or regulated since the 2000s, and the pesticides showing low toxicity and a short retention time are now being used. However, dangerous pesticides continue to be used in many countries, especially developing countries, and the acreage where serious damage has been inflicted have been increasing all over the world.

sheeting buried in soil, which help to maintain nutrients and moisture, exacerbates these problems. In addition, discarded plastic sheeting (500,000 tons/year) spoils the soil by inter‐

A Novel Bioremediation Method for Shallow Layers of Soil Polluted by Pesticides

http://dx.doi.org/10.5772/56153

289

Soil pollution in China is caused by not only pesticides, but also wastewater that is insuffi‐ ciently treated by industry. For example, melamine, which is used for the production of melamine resin, contains a very high level of nitrogen. In 2004-2007, melamine was intention‐ ally added to dairy products by some food manufacturers in China to increase the apparent content of protein. Consequently, serious food-related toxicity occurred in the people, dogs and cats that consumed the dairy products. Wastewater containing melamine was discarded into the environment without any treatment until the incidents occurred. Therefore, the soil, groundwater and crops near the manufacturing facilities were polluted with melamine [17]. A similar incident occurred related to the production of rice in China. Methamidophos, an organophosphorous compound, was mistakenly included in rice, although the precise reason for this accident was not clarified. One million tons/year of food is affected by soil pollution

The shortage of drinking water caused by groundwater pollution is also serious. To avoid groundwater polluted by toxic compounds, wells were dug to much deeper layers in the aquifer [18-19], but the groundwater at these layers contains arsenic and fluoride. Around 25 million people who drank this water showed arsenic toxicity and dental fluorosis. Since the 1980s, poisoning by arsenic has been gradually increased in many countries, such as India,

**3. A novel bioremediation process targeting the shallow layers of soil**

As described in section 2, excess use of pesticides in agricultural fields causes serious pollution of the soil and groundwater. The characteristics of soil pollution by pesticides are that the area of pollution is huge, and the pollution reaches to deep layers. *Ex situ* bioremediation, which is a process performed after movement of the polluted soil, is not adequate to control such widespread pollution. Therefore, *in situ* bioremediation, which involves treating the soil in

Several *in situ* bioremediation processes have been proposed [2], and the ORC method developed by the REGENESIS Corp and bioventing are often used. Figure 2 shows a schematic diagram of these processes. In the bioventing method, air is supplied from the upstream side of the pollutant at deeper layers of soil by using high-pressure pumps. In the ORC method, oxygen release compounds (ORC) are injected into the deeper layer by using high-pressure pumps. The supply of oxygen activates the microorganisms present in the polluted soil,

Bioventing is suitable for the remediation of contaminants at deeper layer and over wide areas of soil, and some projects using bioventing have been performed. For example, bioremediation

rupting the exchange of air and water.

Thailand and Bangladesh [20].

enhancing the degradation rate.

in China according to an investigation by a public organization.

**3.1. Problems with conventional bioremediation processes**

place, had been applied for pollution with pesticides.

#### **2.2. Soil and groundwater pollution by pesticides**

Atrazine and simazine have been used extensively in the United States and Europe. In the United States, 36,000 tons/year of atrazine are still being used in the patties and fields. The fields and rivers in the northwest part of the United States have been monitored for several years, and many kinds of pesticides were detected there [6-9]. In fact, 75% and 40% of samples collected in rivers and groundwater contained atrazine and other harmful pesticides. The concentrations of harmful pesticides were gradually decreased, but the concentrations of diazinon, chlorpyrifos and malathion often exceeded the benchmark value [6].

Atrazine sprayed from the airplanes is often carried by wind to other locations at a distance of over 1000 km from the spraying place, and these fall with rain. As noted above, the EU forbade the use of triazine herbicides, because their concentrations in groundwater exceeded the limit they set for safety standards. However, because the yield of crops can be enhanced by the use of atrazine, the farmers in the EU do not necessarily obey this decision, and harmful pesticides are still used and detected from the river water and groundwater in some countries in Europe [10-12].

Soil pollution is much more serious in the countries in Asia. Although the current amount of pesticide consumption in developing countries is only 25% of the total amount produced, 99% of the people killed by pesticide poisoning are from developing countries. Soil pollution also induces groundwater pollution. As groundwater is used for drinking water without any treatment in many countries in Asia due to the water shortage, this may lead to many human cases of poisoning. Additionally, many kinds of POPs which were produced before 2001 are still used in some countries, even though their use and production is prohibited by the Stockholm Convention. For example, in Vietnam, the soil is polluted by 4 tons of harmful pesticides that were buried in soil to discard them, and 108 tons of toxic POPs are still being stored in a warehouse. Such POPs can be easily obtained at markets in Nepal and India. BHC is still used for the production of crops and cotton cultivation in those countries, because it is cheap and effective [13].

In China, the pollution of soil and groundwater are extremely serious [14-16]. Approximately one-third of the wastewater from industries, and 90% of the drainage from households is directly discharged to the river. It has been estimated that 40% of river water (95% in urban areas) is already impossible to utilize as drinking water due to pollution, and thus, it has the potential to harm the 160 million people who are known to use this water.

The amount of pesticide consumption in China has increased ten times compared to that in the 1990s. Because of excess use (13.4 kg/ha) for agricultural fields, 60% of the pesticides used remain in the soil without degradation. Therefore one-sixth of the agricultural fields need to be remediated. Chemical fertilizers are also excessively used, and approximately 60% of the fertilizer also remains in the soil. Excrement (3 billion tons) discarded in pastures is also present in the soil. These contaminants cause pollution due to nitrate nitrogen. The use of plastic sheeting buried in soil, which help to maintain nutrients and moisture, exacerbates these problems. In addition, discarded plastic sheeting (500,000 tons/year) spoils the soil by inter‐ rupting the exchange of air and water.

Soil pollution in China is caused by not only pesticides, but also wastewater that is insuffi‐ ciently treated by industry. For example, melamine, which is used for the production of melamine resin, contains a very high level of nitrogen. In 2004-2007, melamine was intention‐ ally added to dairy products by some food manufacturers in China to increase the apparent content of protein. Consequently, serious food-related toxicity occurred in the people, dogs and cats that consumed the dairy products. Wastewater containing melamine was discarded into the environment without any treatment until the incidents occurred. Therefore, the soil, groundwater and crops near the manufacturing facilities were polluted with melamine [17]. A similar incident occurred related to the production of rice in China. Methamidophos, an organophosphorous compound, was mistakenly included in rice, although the precise reason for this accident was not clarified. One million tons/year of food is affected by soil pollution in China according to an investigation by a public organization.

The shortage of drinking water caused by groundwater pollution is also serious. To avoid groundwater polluted by toxic compounds, wells were dug to much deeper layers in the aquifer [18-19], but the groundwater at these layers contains arsenic and fluoride. Around 25 million people who drank this water showed arsenic toxicity and dental fluorosis. Since the 1980s, poisoning by arsenic has been gradually increased in many countries, such as India, Thailand and Bangladesh [20].
