الفهرس 
INTRODUCTIONOnly 14 pages are availabe for public view
 |  | from | 185 |  |  |
| | | from | 185 | | |
Abstract
The herbicide glyphosate has been widely used all over the world since it was introduced by Monsanto in 1974, and it is successfully used to control annual, perennial and broad-leaved weeds in various horticultural crops, including citrus. Encouraging this wide use, glyphosate has good stability and toxicity properties. In light of the extensive use of the herbicide, some opinions have emerged calling for it to be important to assess its environmental risks and study its acute and chronic effects on non-target species. Actually, some references have reported that glyphosate may cause some diseases. In 2015, the International Agency for Research on Cancer (IARC) classified glyphosate as ”probably carcinogenic to humans (group 2A) based on its evaluation of some experimental animal studies. This classification has been widely circulated by environmental groups opposed to the extensive use of chemical pesticides, and has called for the use of glyphosate to be restricted or banned. This situation has caused a great deal of debates about the use of glyphosate in many countries. Some studies have confirmed that POEA, which is present in glyphosate formulations as surfactants, is responsible for the confirmed negative effects on human health and the environment. Thus, the countries that were cautious decided to restrict or ban the use of glyphosate and this encouraged the conduct of many studies on evaluation environmental impacts and finding an appropriate alternative to glyphosate in the case of banning or restricting its use, particularly under local conditions. It is known, that there are many models of environmental impact assessments and pesticide risk indicators in the literature, and that these indicators help guide farmers and policy makers to compare the environmental impact of different pesticides and design effective pest control practices with minimal environmental impacts. These indicators usually provide information about the environmental risks of pesticide use in a single section or item. Also, some indicators such as the Environmental Impact Quotient (EIQ) are used globally to assess environmental risks from a broader perspective, as this model includes more than one component (workers/farmers, consumers, ecology).
The previous background formed the idea of the present study to obtain an overview of the behavior and fate of glyphosate and its environmental and health effects under Egyptian conditions, and to evaluate glufosinate ammonium as a suitable alternative if the herbicide glyphosate is restricted or banned in the future. Accordingly, this study aims to:
- Evaluate the efficiency of glyphosate and glufosinate ammonium (as possible alternative) against weeds found in citrus orchards.
- Assay the toxic effects of the most effective commercial formulations of glyphosate and glufosinate ammonium on experimental mice including: acute toxicity tests (estimation of LD50 values), biochemical tests, genotoxicity, molecular genetics and histopathological effects of both herbicides.
- Evaluate side effects of the two herbicides on some non-target organisms, earthworm (Allolobophora calignosa) and honey bee workers (Apis mellifera).
- Determined of residue levels of the two tested herbicides in the treated soil after different periods from application, and calculate the half – life period for each one.
- Carried a risk assessment analysis for each herbicide using EIQ model, and comparing the obtained results to conclude the possibility of recommending the use of glufosinate ammonium as a possible alternative to glyphosate.
The most important results obtained can be summarized as follows:
I- Efficiency of glyphosate and glufosinate ammonium (as possible alternative) against weeds found in citrus orchards
The results showed that both pesticides had a high efficiency against the tested weeds (Bermuda grass, Field Bindweed Annual Sow thistle, and London Rocket), as it gave inhibitory effects on dry weight after 14 days of treatment at the recommended rate, while twice the rate caused a reduction in dry weight after 7 days, Although there are no significant differences between the two tested application rates. The percentage of dry weight reduction increased over time on all types of weeds at both rates, and the highest percentage was after 7 and 14 days of application.
Ⅱ-Toxic effects of the most effective commercial formulations of glyphosate and glufosinate ammonium on experimental mice (acute toxicity/ LD50 values, biochemical effects, genotoxicity, molecular genetics and histopathological effects)
A-The Medium lethal-dose (LD50 values)
The results of toxicity against experimental mice treated after acute exposure showed low toxicity for glyphosate, where the values of the LD50 was (3790.30 mg/kg), while the LD50 value of glufosinate ammonium was (1306.25 mg/kg).
B-Biochemical effects
The biochemical parameters of liver function (AST&ALT) and kidney function (creatinine & urea) of treated mice after 14 and 28 days of exposure showed that exposure to tested dose of both herbicides led to an increase in AST and ALT enzyme activity to varying degrees after the two exposure periods. Also, the parameters of kidney function showed an increase of creatinine and urea than the control group. Meanwhile, this increase did not differ significantly between exposures to a period of 14 days from that of a period of 28 days. The increase in liver and kidney function parameters differed among the two pesticides, as exposure to glufosinate ammonium led to a greater increase in these values than glyphosate.
C - Histopathological effects
The histopathological effects on the brain were shown in mice exposed to both pesticides that there was no change observed generally than the normal histological structure for the cerebellum and subiculum. In contrast to some other brain components in which the effects of glyphosate and glufosinate ammonium were varied. Similar effects of both herbicides on the liver were observed.
D – Genotoxicity effects
The test results for sperm abnormalities after 14 and 28 days of exposure showed significant mutagenic effects of glufosinate ammonium more clearly than glyphosate at the tested doses, while there were no significant differences in the mutagenic effects of the micronucleus abnormalities test. The same results were confirmed to test for chromosomal aberrations when exposed to the tested doses.
E - Molecular genetic effects
Glyphosate showed stimulating effects on the activity of BDNF and TNFα genes associated with brain inflammation, while the activity of TrkB gene of glufosinate ammonium was higher compared to glyphosate. On the other hand, glyphosate showed an inducible effect on the activity of IL-1ß, COX-2 and IL-6 genes associated with hepatitis than glufosinate ammonium.
Ⅲ - Evaluation of the side effects of the two herbicides on some non-target organisms (earthworms and honey bee workers)
A- Earthworms
The results of the acute toxicity test using filter paper after 48 hours showed that glufosinate ammonium (LC50 = 1.06 mg/cm2) has a lower toxic effect than glyphosate (0.95 mg/cm2 = LC50). While the results using artificial soil showed a significant loss in biomass and loss in the number of juvenile larvae at high concentrations of both herbicides, in contrast to low concentrations. On the other hand, the results of the chronic toxicity test showed a significant loss of biomass and a loss in the number of juvenile larvae of earthworms with high concentrations of both herbicides in contrast to low concentrations. It was observed that the toxicity of glufosinate ammonium (LC50=3340.35 mg/kg) to earthworms was higher than that of glyphosate (LC50= 3944.9 mg/kg).
B- Honey bee workers
The results obtained in the acute and chronic toxicity tests showed that both herbicides at the tested concentrations had no toxic effects on honey bees.
Ⅳ- Determining the residual levels of the tested herbicides in the treated soil after different periods of application, and calculating the half-life for each of them
The presence of glyphosate residues was detected after 3 days of treatment in the three tested soil depths (0, 10, and 25 cm). The herbicide disappeared after 7 days at a depth of zero, while at a depth of 10 and 25 cm, the pesticide disappeared after 7 and 14 days, respectively. No residues of glufosinate ammonium were detected in the soil after 14 days of treatment in the three tested soil depths. The half-life at a depth of 10 cm for glyphosate and glufosinate ammonium was 0.43 and 0.37 days, respectively.
Ⅴ- Risk assessment analysis for each herbicide using the EIQ model
A – Glyphosate herbicide
The calculated values towards workers, consumers, and the ecology amounted to 31, 6, 8, respectively. With a total value of 45 corresponding to the value of EIQ 15, and the rate of using the two EIQ FUR fields 14.25.
B- Glufosinate ammonium
The calculated values towards workers, consumers, and the environment amounted to 47, 7, and 13, respectively. With a total value of 67, corresponding to an EIQ value of 22.3, and a field usage rate of 8. 92.
The comparison between the previous results indicated that the values of glufosinate ammonium less than those values were calculated for glyphosate.
Conclusion & Recommendations
The results of the toxicological tests showed different effects of both herbicides on exposed mice to the tested doses than untreated, represented by changes in some biochemical parameters indicative of liver and kidney functions, abnormalities in sperm cells, and effects that stimulated the activity of some genes related to brain and liver inflammation. Histopathological study confirmed convergent changes in brain and liver tissues. Conversely, the analysis of the results of the risk assessment for both pesticides using the Environmental Impact Quotient (EIQ) model showed a moderate Field Use Rating (EIQ FUR) value for glyphosate, and a low rate for glufosinate ammonium, which indicates that it is safer in terms of the environmental impact quotient than Glyphosate, and that it can be used as an alternative for it in case of restriction or discontinuation of its use on orchards and other crops. These results confirm the importance of recommending users and applicators of both herbicides to take into account safety procedures and use protective clothing and tools to avoid exposure to each herbicide, in addition to adhering to good agricultural practices when using them.