Aquatic Toxicity Of Some Pesticides Used In Sugar Cane Factories In Colombia

1. Introduction
A small fraction, estimated at <1 to 2% of the pesticides applied to crops are lost from fields and enter nearby streams during rainfall events. In many cases aquatic organisms are exposed to mixtures of chemicals, which may lead to greater non-target risk than that predicted based on traditional risk assessments for single chemicals

Pesticides vary greatly in toxicity. Toxicity depends on the chemical and physical properties of a substance, and may be defined as the quality of being poisonous or harmful to animals or plants. Poisons have many different modes of action, but in general cause biochemical changes which interfere with normal body functions.
The toxicity of any compound is related to the dose. A highly toxic substance causes severe symptoms of poisoning with small doses. A substance with a low toxicity generally requires large doses to produce mild symptoms. Even common substances like coffee or salt become poisons if large amounts are consumed.
Toxicity can be either acute or chronic. Acute toxicity is the ability of a substance to cause harmful effects which develop rapidly following absorption, i.e. a few hours or a day. Chronic toxicity is the ability of a substance to cause adverse health effects resulting from long-term exposure to a substance.

Measuring Acute Toxicity (LD₅₀ And LC₅₀ Values)
Acute toxicity of a pesticide refers to the effects from a single dose or repeated exposure over a short time (e.g. one day), such as an accident during mixing or applying pesticides. A pesticide with a high acute toxicity can be deadly even if a small amount is absorbed. Acute exposures may be referred to as acute dermal, acute oral or acute inhalation poisoning. Usually the effects of acute exposure, if any, occur within 24 hours.

LD₅₀ or Lethal Dose 50
The LD₅₀ is the dose of a pesticide that will kill half of a group of test animals from a single exposure by either the dermal, oral or inhalation routes. The larger an animal, the greater the lethal dose required to kill it. The LD₅₀ is expressed in milligrams per kilogram of body weight of the test animal
A pesticide with a lower LD50 is more toxic than a pesticide with a higher number because it takes less of the pesticide to kill half of the test animals. The smaller the LD₅₀ value, the more toxic the pesticide.

LC50 or Lethal Concentration 50 .
The LC₅₀ value is a measure of the toxicity of a pesticide when test animals breathe air mixed with pesticide dust, vapors or spray mist. The LC₅₀ is the concentration of pesticide which is lethal to 50% of a population of test animals and is usually determined for a specific exposure period (e.g. inhalation for 4 hours). The length of exposure is important because shorter exposure periods generally require higher pesticide concentrations to produce toxic effects. LC50 values for pesticides in air are expressed as the ratio of pesticide to air, in parts per million (ppm) or parts per billion (ppb). LC₅₀ values are also determined for fish and aquatic organisms based on the concentration of pesticide in water for exposure periods of 24 to 96 hours.

2. OBJETIVES

2.1 General objective:
To evaluate the acute toxicity of some pesticides used at a Sugar cane Factory in pests control and general agricultural activities.

2.2 Specific objectives:
1. To establish for the Diuron and 2, 4 D, the LC₅₀ or Lethal Concentration 50 .
2. To establish the acute toxicity to a mixture of Diuron and 2,4D pesticides.
3. To establish the acute toxicity of a real mixture (formulation) apply to the sugar cane.

METHODOLOGY
In order to reach the objectives proposed the following methodology will be carried out:
1. To standarize the methodology for determination of the pesticide toxicity :
-To realize a bibliographic review and to choose the best methodology to apply at research conditions.
-To acclimate native species (Daphnea pulex) to realize the bioassays.
-Realize bioassays to determinate the optimal analysis conditions.

2. To determinate the LC50 values for the pesticides Diuron and 2,4 D

3.To determinate the toxicity of a real mixture of pesticides (formulation ) used at the sugar cane factory

UNIVERSIDAD DEL VALLE
Ingeniera Sanitaria y ambiental
Ciudad Universitaria Melendez
Calle 13 No 100-00
Sede San Fernando
Calle 4B No 36-00
PBX +57 2 3212100 A.A. 25360
Cali - Colombia

Bleny Hélène
7, rue du docteur Feuerbach
68130 Altkirch – France
helene.bleny@epfl.ch