Public health implication of indiscriminate use of herbicides

Introduction

Recently there has been a widespread use of herbicides for the elimination of bushy surrounding and farmlands. Due to its ease of usage and reduce manual effort involved, many people has embraced it without due consideration on its effect on health and the environment. These effects include pollution of the environment, water bodies and indiscriminate destruction of biodiversity.

In Nigeria the population is increasing leading to a geometrical increase in herbicide users due to the fact that majority of the inhabitants are student who as a result of their knowledge on the convenience of using herbicides for removal of weeds opt for it as less manual labour is required. The users are also found agriculture, medicine, industries and various household. Over 80 (eighty) percent of the herbicide sprayed out by the users reaches a destination other than then target species including non target species like air, water, bottom sediment, food plant, animal and human.

However, majority of herbicide users lack the knowledge of the toxicity of the herbicide. They do not follow appropriately the descriptive label in the herbicide can/containers so when they applied it the public health and the environment are been altered. They also lack proper method to apply this active ingredient to the target area so as to get positive result at the end.

Moreover, those that are trained on the ways or method to formulate these herbicides do it with greed. The characteristic of this herbicides are meant after their formulation, majority of them don’t have protective wears that protect them of hazard these herbicides will cause to them.

Also those that are not license by the law to formulate these herbicides are involving themselves in it. This can be notice at the end of their production that the herbicides do not control/kill target species, the containers/ cans that contain these herbicides lack labels, expiring date, manufacturing date, National Agency for Food and Drugs Association Commission (NAFDAC) Number and in case of those that has label the proper direction on how to applied it is not inscribed on it.

Although, despite the educational background of some herbicide users they misuse the herbicides. The one meant for a particular target species will be use for another target species and vice versa. Greatest hazard occur to herbicide users when opening, mixing and applying it to the target area. Unfortunately they may be the one who is least concerned either because of lack of information or because they have become complacent from repeated use. Other hazard associated to the usage are; alteration of the normal physical environment like air, water, soil, plant, animals (bird, aquatic life, amphibians) household pest died due to ingestion of herbicide that is not properly applied. Some of the effects associated to the exposure to these herbicides are headache, dizziness, nausea excessive sweating etc.

Conceptual framework

According to Gross (2000), herbicide users need to have adequate knowledge of the herbicide they are about to use to control weed so that the proper one can be applied to the target species. Graeme (2005) stated that herbicides can be characterized as follows:

• Herbicides are usually made up of active ingredients that kill the target weed
• Toxicity to target weed
• Toxicity to other weeds
• Generally poisonous to man
• Generally have varied lethal dose
• Generally lose their potency when wrongly stored
• It is acidic
• Persistence on the environment

Types of herbicides

Adesigbin (2007) opined that there are different different types of herbicides and they are all designed to kill plant tissue. However, they accomplish it by two basic methods. They are known as contact herbicides and systemic herbicides.

1. Contact herbicides: Contact is a word that means the chemical in that specific type of herbicide will kill the parts of the plant it contacts. For broadleaf weeds this means it will kill the above ground leafy part of the plants. It will not directly kill the below ground plants parts, such as roots, bulbs, tubers, or rhizomes. Contact herbicides are popular because they work quickly by killing the tissue in as fast as one day. Some herbicides will combine contact with systemic chemicals for a faster effect. For some plants, killing the above ground portions will not be enough to wipe out the plant completely. Most plants will re-grow plant tissue and the herbicide will need to be reapplied. However, each time the plant has to use energy to start growth again will weaken the plant and eventually kill it.
2. Systemic herbicides: For systemic types of herbicides, the word “Systemic” means the plant absorbs through the leaves or stems and transports it internally throughout the plant. The chemical travels with the sap so it usually doesn’t have the quick “knockdown” effect. The greatest benefit of a systemic type of herbicide is that it will kill the entire plant, roots and all. The speed of chemical movement in the plant is largely dependent on soil and air temperature. A chemical sprayed in early spring may take a couple weeks longer to work than the same chemical sprayed in mid-summer. The speed of kill is also dependent on the “mode of action” of the chemical (how the chemical works inside the plant).

Banned herbicides

The Federal Ministry of Environment (2005) revealed a list of banned herbicides, these includes: Haptachor, flouroacedtamide, chlordane, mercury compounds, ethylene 1,2 dibromide, chlordimeform, Dinoseb and Dinoseb salts, dichlorodiphenxyl Trichloroethane (DDT), Pentachlorophenyl, Chlorobeniophate, Aldrin, Dieldrin, Methanridophus, methyl parathion, parathion and paraquate while the under listed are under severe restriction:

Lindane, captofol, hexachlorobengene and phosphamidom.

Herbicide formulation

Adesigbin (2007) identified that herbicide are formulated for use in various way that will allow the users to apply it to the target weed. These could be formulated in the following ways:

• Wettable powder: These are dry powder that contained herbicides which can be mixed with water to form liquid or suspension. When using wettable powder one must shake the sprayer frequently to disallow the nozzles/strainers of the sprayer from being clogged with powder that may settled at the bottom of sprayer. These are prepared by adding active ingredient to sine solvent such as kerosene/diesel.
• Dust: These are grounded herbicides that are already mixed which contain different percentages of active ingredients.
• Granule: This formulation varies in shape and size and is usually prepared by spraying solution of the herbicide into performed granular carrier. Some materials are easily moved by wind or water for example pirimicarb.
• Fumigant: They are liquid or dust which change into gas when released can kill weeds

Influence of herbicide use to man’s environments

Air: According to Miller (2004) herbicides can contribute to air pollution. Herbicide drift occurs when herbicides suspended in air as particles are carried by wind to other areas potentially contaminating them. The Federal Environmental Protection Agency (2007) observed that herbicides that are sprayed on to field and used to fumigate soil can give off chemicals called volatile organic compounds which can react with other chemical and form a pollutant called ozone.

Water: Barbaxhg, Crawford, Gilliom, Hamilton, Martin, Nakagaki, Nowell, Scott, StackeIberg, Thelin and Wolock (2007) stated that herbicides were found to pollute every stream. Herbicides residues have also been found in rain and ground water, that the concentration exceeds those allowable for drinking. Goss (2000) said that there are four major routes through which pesticide reach the water. It may drift outside of the intended area when it is sprayed kit may percolate or lead through the soil it may be carried to water as runoff or it may be spilled for example accidentally or through neglect.

Soil: Borrow, Engelhaupt, Fox, Gulledge and Mclachlan (2007) saw that many chemicals used in herbicides are persistent soil contaminants whose impact may endure for decades and adversely affect soil conservation. The use of pesticide decreases the general biodiversity in the soil. Goss (2000) opined that it help to increase the yields for farms in drought years, when organic farm have yield 20-40% higher than their conventional counter parts. A smaller content of organic matter in the soil increase the amount of herbicides that will leave the area of application because organic matter binds to and help break down herbicides.

Plant: Nitrogen fixation which is require for the growth of higher plants is hindered by herbicides in soil. It also interferes with legume rhizobium chemical signaling. Reduction of this symbiotic chemical signaling result in reduced nitrogen fixation and thus reduced crop yields (Rocket 2007).

Animals: According to Miller (2004) herbicides inflict extremely widespread damage to biota many countries have acted to discourage pesticide usage through their biodiversity action plans. Animals may be poisoned by herbicide residue that remain on food after spraying for example when wild animals enter sprayed fields or nearby areas shortly after spraying. Goss (2000) reported that widespread application of herbicides can eliminate food sources that certain types of animals need, causing the animals to relocate, change their diet or starve. Poisoning from herbicides can travel up the food chain for example birds can be harmed when they eat insects and worms that have consumed herbicide chemicals. Fish and other aquatic biota may be harmed by herbicide contaminated water, herbicide surface runoff into river and streams can be highly lethal to aquatic life. When they are applied into water to kill plants they are toxic to fish and other water animals at concentrations similar to those used to kill plant (Cone 2000). Bingham (2007) revealed that application of herbicides to bodies of water can kill off plants on which fish depend for their habitat. It can also accumulate in water bodies to a level that kill off zooplankton, the main source of food for young fish.

Persistent organic pollutants

Persistent organic pollutants (POPs) are compounds that resist degradation and thus remain in the environment for years. Some POPs are aldrin, chlordane, DDT, etc, POPs have the ability to volatilize and travel great distances through the atmosphere to become deposited in remote regions. The chemicals also have the ability to bioaccumulation and biomagnify and can bioconcentrate up to 70000 times their original concentration. POPs may continue to poison non target organism in the environment and increase risk to humans. (Well 2007).

Public health implications

According to Leiss and Sanvitz (2000) all herbicides must be considered potentially toxic to humans. The hazard in the use of herbicide materials lies in failure to follow precaution and direction for use as indicated on the label or unexpected accident such as the bursting of spray hoses breaking or rusting of herbicide container and careless storage or improper disposal of containers. This will be expatiates under the following area:

• herbicide toxicity and exposure
• Symptoms of herbicide poisoning

Herbicide toxicity and exposure

Leiss and Savitz (2000) observed that hazard or risk of using herbicide is the potential for injury or the degree of danger involved in using a herbicide under a given set of conditions. Hazard depends in the toxicity of the herbicide and the amount of exposure to the herbicide and is other illustrated with the following equation HAZARD = TOXICITY EXPOSURE. The toxicity of a herbicide is a measure of its capacity or ability to cause injury or illness. The toxicity of a particular herbicide is determined by subjecting test weeds to varying dosage to the active ingredient and each of its formulated products. They also continue that the harmful effects that occur flow a single exposure by any route entry are termed “acute effects”. The chrome toxicity of herbicide is determined by subjecting test weeds to long term exposure to the active ingredient. Any harmful effects that occur from small doses repeated over a period of time are termed “chronic effect”.

Symptoms of herbicide poisoning

White (2000) advanced that the symptoms of herbicide poisoning progress through several stages.

• Mild poisoning: These include fatigue headache, dizziness, numbness in the arms and legs, nausea and vomiting, excessive sweating and salivation abdominal cramps and diarrhoea, loss of appetite, feeling of sickness, urination of the skin, eyes, nose and throat.
• Moderate poisoning: This include the inability to walk, generalized weakness difficult in talking, muscular twitches contraction of the pupil of the eye, vomiting difficulty in breathing, nervous distress.
• Severe Poisoning: Severe contraction of the pupil of the eye, secretion from the mouth and nose, convulsion, respiration collapse, unconsciousness, loss of pulse and death.

Precautionary measures to herbicide users

Well (2007) reported that whenever we are making use of herbicides the most important consideration is safety. The safety includes safety of the users, safety of other people, safety of the domestic animals and the environment in general. The following entail the possible heading on precautionary measures to herbicide users.

• Personal protective equipment (Petreman, 2007)
• Herbicide labelling (Adesigbin, 2007)
• Measures in applying herbicide (Miller, 2004)
• Health Education (White, 2000)

 Personal protective equipment

Personal protective equipment ate equipment which should be worn by the operator or spray men prior to the application of herbicides example are hand gloves (disposable and non disposable) apron-nylon type, overall safety shoes (rain boot), nose mask, face cap/helmets, goggles, respirator, trouser/long sleeve shirt etc. The reason for wearing protective materials cannot be over emphases this includes:

• To prevent slippery or falling down by the operators
• To avoid soiling of the body with herbicides
• To reduce prolong contact with the herbicide
• To prevent ingestion of herbicides directly or indirectly (Petreman 2007).

Herbicide labelling

Adesigbin (2007) opined that herbicide labelling is the most important way of getting information regarding the handling and use of any particular herbicide. It is therefore a good importance that before commencing the use of any herbicide the label must be read carefully and all points covered by it must be understood.

He also continues by saying that label is usually in three sections:

• The first section: This contains the technical information on the herbicides and it will include the following:
• The trade/brand name of the herbicide. This will relate to the company producing the product.
• The active ingredient of the product this aspect will explain the component of the active ingredient of such product.
• Formation types: Different formulation required different handling during the mixing. This aspect will explain how the product was formed.
• The name and address of the manufacturer.
• The registration number of their product will be indicated to show that the product has been cleared with the government e.g. NAFDAC REG NUMGER.
• Second section: This section contains detailed instructions on how and when to use the product/herbicide.
• How to mix the product: this will indicate any special instruction on how to mix the product.
• How to apply the product: This will concentrate on the application rate to be use for a particular pest.
• Where to apply the product and how frequent.
• Third section: This will explain the handling the product. It will also indicate the storage and disposal of the product. It will also explain the environmental hazard of the product.

Measures in applying herbicide

Miller (2004) identified measure to put into consideration before and when applying herbicide and they are:

• Always read the instructions on the label of any herbicide. Never accept any herbicide if the label is missed.
• Always wear the protective wears.
• Do not mix the herbicide with bare hands.
• Avoid transportation of herbicides with food items because the danger of contamination.
• Operators with scratches on the skin should not apply the herbicides.
• Herbicides should not remain in the spraying equipment to avoid rusting of the sprayer and chemical pollution from the left over chemical in the spraying machine.
• Herbicides packet, spray mixed, sprayers empty container contaminated clothing should not be left unattended.
• Wash thorough immediately after the mixing or after spraying because of exposure of herbicides.
• Operator should not face the windward direction when spraying.
• Any spraying areas should be marked by warning sign “X” as hazard area.

Aibor and Olurunda (2006) also highlighted some measures due to the use of herbicides and they are:

• There should be availability of soap and water for the operator to wash the skin and cloth after the work.
• Remove all food items before the application of herbicide.
• Avoid too much exposure to herbicide.
• Always avoid blow of blocked nozzle with month to avoid injection of herbicide.
• Always empty all containers of herbicide used safely.
• Operator should avoid smoking or eating when applying herbicides.
• Herbicides should be store into the original container. The practice of decanting pesticide from the original container into another container should be discouraged.
• All domestic animal and man should be kept away from any spraying area.

Health education

Well (2007) suggested that to reduce the influence of herbicide use on our environment and the health of the public at large the users both domestically and commercially should be health enlighten so that they can get adequate knowledge of the so called “herbicides” which is very hazardous. He said that method to pass the information to the users is through the mass media like television, radio, newspaper, poster, internet etc. These medium will cover a large number of the hazard associated with it.

Herbicides users have co-operative society that helps to regulate their activities. This co-operative group is a medium to disseminate health information to members on the effective ways in the production and application of herbicides. This medium can also help them to demonstrate the right practical skills. This approach can also include organizing workshop, seminars, conference, symposium etc. To health enlighten the users of the after math of poor precautionary measures in the production and application of herbicides (White 2000).

References

Adesigbin K.R (2007). Essential of pest management and entomology 1^st edition, published at Ibadan in typeset and printed WONAK Ventures. Page 48-51.

Aibor M.S and Olorunda J.O (2006). A technical hand book of environmental health in the 21^st century for professional and students 1^st edition published at Akure by this mercies publisher. Page 35-46.

Barbash E.J, Grawford G.G Gillion J.R, Hamilton A.P. Martin D.J, Nakagaki N, Nowel H.L, Scott C.J, Stackelberg E.P, Thelin G.P and Wolock D.W (2007) quality of our nation water: pesticides in the nation streams and ground water published by U.S-Geological survey page 4.

Bingham S (2007) Pesticides in river and ground water published by the U.K, Environmental agency. In U.K, Page 89, 122, 156 and 200.

Borrow E.M, Engelhaupt E, Fox E.J, Gulledge J, and Milachlan A.J (2007) “Pesticide reduce symbiotic efficiency of Nitrogen-Fixing rhizobia and host plant”. Proceedings of National academy of science for the U.S.A. Published in Californian Page 104.

Cone M, (2000) “A wind-borne threat to sierra frogs”. A study finds that pesticides used on farms in the San Joaguin Valley damage the various systems of amphibians in Zosemite and elsewhere L.A Time. Published in china. Page 4-15.

Gross D.W (2000). Environmental indicator of pesticide leaching and runoff from farm fields. Published by the United States department of Agriculture. Washington. Page 88-93.

Graeme Murphy (2005) Resistance management-pesticide rotation. Published by the Ministry of Agriculture, Food and Rural Affairs, Published in Ontario at U.S.A. Page 67.

Leiss J.K and Savitz A.S (2000) “Home pesticide use and childhood cancer”. A case control study, American Journal of Public Health. 85: 219-252.

Miller G.T (2004) Sustaining the earth 6^th edition. Thompson learning, pacific grove, published California. Page 211-216.

The Federal Ministry of Environment (2005) Policy guidelines on pest and vector control. Published by the Federal Republic of Nigeria. Page 13-20.

Wells M (2007) “Vanishing bees threaten U.S crops”. Published from BBC News at U.K (in English).

White head R (2000) “The U.K pesticide guide”. Published in cabi at American.

Zeissloff Eric (2001) “Schadet imidacloprid den bienen”. Published from BBC News at Germany (in German).