5.7.1. Background and Sources: Pesticides
Pesticides are diverse, primarily including insecticides, herbicides, fungicides and rodenticides. Pesticides enter water bodies from a number of different pathways. They are applied directly to control aquatic nuisances such as water hyacinth. They can be components of runoff from residential, agricultural, and other commercial applications. They also come from the atmosphere, usually attached to particles. As a consequence, pesticides are widespread in residential, urban, and agricultural areas. Pesticides are very different in their chemistry and environmental fate, in large part because pests are also diverse. Target species include mold, bacteria, rats, spiders, barnacles, mosquitoes and more, and each species has a metabolism that is vulnerable to different chemicals.
Pesticide manufacture and use has evolved significantly towards protecting the environment since the times when lead and arsenic compounds were dusted in homes to control insects (Baird 1995). Efforts have been made to create pesticides that can specifically target the pest and that can degrade after their function has been performed. However, pesticides that were used historically continue to be environmentally important because of their persistence.
Organochlorine compounds (OC’s; molecules containing carbon and chlorine) were introduced in the 1930s and bear some similarity to PCBs in their characteristics and environmental fate. They were effective for long periods of time against insects in homes, institutions, crops, and livestock, largely because they were nearly non-degradable. Because of their longevity, these compounds remain in the environment today despite being regulated and removed from manufacture up to forty years ago. Several organochlorine compounds and their degradation products are the focus of this review because of their environmental significance and the availability of historic data.
It is important in the future to also evaluate pesticides currently used, which tend to be less persistent but more toxic. The varied land uses in the LSJR basin, along with its extensive recreational and commercial maritime activities, cause a broad spectrum of pesticides to be loaded into the river. The U.S. Army Corps of Engineers directly applies herbicides 2,4-D, diquat, and glyphosate in the southern parts of the river for the control of water hyacinths and water lettuce (USACE 2012). The city of Jacksonville sprays malathion, organophosphates, and pyrethroids for mosquito control (COJ 2010). Agriculture in southern LSJR contributes to the pesticide load as well. While estimates of current total pesticide loading rates into the LSJR are elusive, it is reasonable to suppose that some of the most commonly detected pesticides in agricultural, residential, and urban U.S. streams (Gilliom, et al. 2006) will be present in the LSJRB. These include the herbicides atrazine, metolachlor, simazine, and prometon, as well as the insecticides diazinon, chlorpyrifos, carbaryl, and malathion. Finally, the tributyl tins used by the maritime industry should be reviewed. These common pesticides represent 11 different classes of chemical structures that will have very different fates and impacts on the environment.
In this study, four organochlorine pesticides and their primary degradation products were assessed. These compounds were primarily used as insecticides and removed from market in the 1970s. Aldrin was used against termites and other insects in urban areas. Dieldrin is a degradation product of aldrin, and was also used directly against termites. Endrin targeted insects and rodents, usually in agriculture, and endrin aldehyde is its degradation product. Heptachlor and its degradation product, heptachlor epoxide, are used here as markers for chlordane contamination since the complex chlordane mixtures are difficult to compare across years and analytical methods. Chlordanes were used in agriculture and in households, especially for termite control. Finally, the notorious insecticide dichlorodiphenyltrichloroethane (DDT) and its degradation products, dichlorodiphenyldichloroethylene (DDE) and dichlorodiphenyldichloroethane (DDD) are also reviewed.
5.7.2. Fate: Pesticides
OCs such as DDT, aldrin, dieldrin, endrin, chlordane, and benzene hexachloride exhibit low volatility, chemical stability, lipid solubility, and a slow rate of biotransformation and degradation. In many cases, the biotransformation products inside the organism could exhibit similar toxicity as the original parent chemical; such is the case for DDT and its biotransformed metabolites, DDE and DDD. This class of insecticides proved to be highly effective and persistent, which was ideal for remediating target pests, but resulted in very long term environmental impacts. These chemicals also have broad spectrum toxicity, meaning they can affect a variety of species, including non-target species. Additionally, like PCBs they can biomagnify up the food chain and resist chemical breakdown in the environment (Woodwell, et al. 1967). Because of their chemical structure, OCs primarily partition into the fat tissue of biota and primarily the organic fraction of sediment. A biomagnification assessment in the Carmans River Estuary demonstrated significant biomagnification of DDT up the food chain (Woodwell, et al. 1967). During its peak use, DDT led to a decline in populations of several bird species, such as the bald eagle and the peregrine falcon.
After the ban of OCs, anticholinesterase insecticides such as organophosphates (OPs) and carbamate esters (CEs) were primarily used. This class of insecticides undergoes extensive biotransformation and is therefore considered nonpersistent, relative to the earlier insecticides. These insecticides are water soluble and can remain in the water column and/or can be taken up by organic matter such as plants and animals. Karen, et al. 1998 reported the removal of the OP insecticide, chlorpyrifos, from the water column and accumulation in the plant, Elodea densa, after a two-week period.
Pyrethroids are the newest (1980s) major class of insecticide accounting for one third of the world’s pesticide application, and are derived from the extract of dried pyrethrum or chrysanthemum flowers. Pyrethroid use has increased with the declining use of OPs (Baskaran, et al. 1999). Although, pyrethroids are more hydrophobic than OPs, they only minimally accumulate in the environment and do not biomagnify (Phillips, et al. 2010). Pyrethroids do, however, quickly adsorb to sediment when they enter the aquatic environment (Miyamoto and Matsuo 1990). Benthic organisms that inhabit the sediment and porewater may be more at risk for exposure to pyrethroids than pelagic organisms.
5.7.3. Toxicity: Pesticides
Due to their prevalence in the LSJR and toxicity, this review will focus on insecticides. Insecticides generally act as neurotoxicants (poison nervous system) to aquatic organisms, although the toxic mechanisms differ between classes (Karami-Mohajeri and Abdollahi 2011). OCs, such as DDT, mainly affect sodium channels in the axons of nerve cells, causing them to remain open for longer than normal (Karami-Mohajeri and Abdollahi 2011). This results in continual excitability of the nervous tissue. In addition to damage to the nervous system, OCs have also caused reproductive effects in exposed organisms. Since Lake Apopka, FL became polluted with difocol and DDT from various sources, including a pesticide spill in 1980 and agricultural and urban runoff, the wildlife inhabiting the area has suffered severe effects. Due to the biomagnification capabilities of these contaminants, animals at the top of the food chain were most affected. Alligator populations declined due to adverse reproductive outcomes, such as reduced phallus size in males, abnormal ovarian morphology in females, modified sex steroid concentrations in both sexes, and reduced hatching success in alligator eggs (Guillette Jr., et al. 1994; Guillette Jr., et al. 1999). Similar effects have been observed in juvenile alligators from another Florida lake, Lake Okeechobee as well (Crain, et al. 1998). Further, Rauschenberger, et al. 2004 suggested that yolk OC burdens were predictive of maternal tissue burdens and that some OCs are maternally transferred in the American alligator. After exposure to the OC insecticides, methoxychlor and DDE, accumulation of the contaminants in the ovaries of female bass and an inhibition of sex steroids were reported (Borgert, et al. 2004). DDT and other chlorinated pesticides were found in the livers of largemouth bass collected from the LSJR (Sepúlveda, et al. 2002). Gelsleichter, et al. 2006 reported an elevated liver OC concentration in the livers of stingrays collected from Lake Jesup, in the SJR. Further, they concluded that stingray reproduction was still occurring; however, elevated serum steroid concentrations and white blood cell counts were noted, suggesting that endocrine and immune function may be altered.
The anticholinesterase insecticides have a reduced mammalian toxicity, as compared to OCs. They act by inhibiting acetylcholinesterase, which is the enzyme that destroys acetylcholine, resulting in continual stimulation of electrical activity in the nervous system. OPs are generally more effective than CEs, but they also have been shown to affect more non-target organisms. Karen, et al. 2001 reported a significant decrease in brain acetylcholine activity and vertebral yield strength in the estuarine fish, Fundulus heteroclitus (commonly found in the LSJR) after exposure to environmentally relevant concentrations (in many areas) of the OP insecticide, chlorpyrifos.
Pyrethroids have an extremely low toxicity to birds and mammals and are less susceptible to biotransformation when ingested; however, they are very toxic to invertebrates and fish. As compared to the other insecticides, they are more specific in the species they target, including a range of household, veterinary, and post-harvest storage insects; and only few chronic effects have been reported as a result of exposure. The primary site of pyrethroid toxicity is the sodium channels in the nerve membrane (Gordon 1997), resulting in repetitive neuronal discharge (similar to DDT). The sodium channels are modified by either preventing inactivation or enhancing activation of the sodium channel when it is at rest (Zlotkin 1999). This action of pyrethroids results in paralysis, collapse, and inhibition of the righting reflex (Moskowitz, et al. 1994). Secondary toxicity to aquatic organisms, such as blue-gill and fathead minnow, has been reported, including disruption of ion regulation at the gill and decreased respiration (Bradbury and Coats 1989). The amphipod, Hyalella azteca has been shown to be extremely sensitive to pyrethroids (Ding, et al. 2010), possibly due to their high lipid content, and thus greater ability to store pyrethroids, relative to other organisms (Katagi 2010).
More toxicological data is needed to discern the effects of the contaminants in the LSJR on the organisms that reside there. The water chemistry in the river could modify the toxicity of many of the contaminants present. However, in many instances more than one type of contaminant has been shown to simultaneously occur. The degree to which exposure to elevated concentrations of multiple contaminants may affect aquatic life in the LSJR is unknown. It is clear that contaminant accumulation has occurred in several species inhabiting the LSJR, therefore the possibility of deleterious effects remains.
5.7.4. Status and Trends: Pesticides in Sediments
Organochlorine pesticides have been found all throughout the LSJR sediments for years (Figure 5.47), an expected outcome given their history of use and persistence. Like PCBs, pesticides were most prevalent in Area 1, the western tributaries, which contained the most sediments with concentrations that exceeded the pesticide PELs. However, the overall detection rate, exceedance rate, and pesticide toxicity pressure is much less than that of the PCBs. Even in the western tributaries, the toxicity quotient was less than one, and in the rest of the river, cumulative toxicity pressure from organochlorine pesticides is fairly minimal with a toxicity quotient close to 0.2. The organochlorine pesticide most responsible for toxicity pressure in the river is DDD, a degradation product of DDT, but in some years and regions, heptachlor and dieldrin were also important (Figure 5.48).
5.7.5. Summary: Pesticides
Organochlorine pesticides are present in the LSJR sediments, mostly at levels that might not cause significant adverse impacts on the benthic ecosystems, but that may add to the overall toxic burden of sensitive organisms. As with many other contaminants, the Cedar-Ortega system is the most contaminated area (Ouyang, et al. 2003). The DDT compounds were found most frequently and at the highest levels, compared to the other organochlorine pesticides. They exerted the most toxic pressure, though dieldrin and heptachlor were also significant in recent years. Previously, the STATUS of organochlorine pesticides in sediments was unsatisfactory while the TREND was unchanged; however, pesticides were not evaluated in this year’s report.