A methodological approach to estimate risks to human health from the use of pesticides in agriculture

This paper presents a simplified methodology to estimate risks to human health from the consumption of drinking water contaminated with pesticides used in agricultural areas. The methodology was applied to estimate the peak and average (long term) concentrations of pesticides in the waters of Lake Taka, lying south-east of Tripoli, in the municipality of Tegea. The Lake presently dries out in the summer months but plans are underway to restore the Lake to a minimum water volume of 12 million m(3). The Lake lies in the middle of a heavily irrigated agricultural area and has a cathment area of 92 km(2). Data were collected on the meteorological conditions, types of soil, irrigation methods, types and areas of crops, pesticide use, anthropogenic activities and ecosystems. The types, quantities, application rates and application times of pesticides applied to land were recorded. For each pesticide chemical and toxicological data were collected from data banks. An initial risk ranking of pesticides, was done by estimating the peak concentration of each pesticide in the surface runoff from the agricultural land, immediately after its application to crops and in combination with an intense rainfall event (worst case scenario). The loss of pesticide to surface water is caused by spray drift directly on the surface of the water and by leaching due to runoff. Predicted maximum concentrations in surface water exceeded by up to 2 orders of magnitude the limit concentrations for drinking water and by up to 1 order of magnitude the limit for drinking water abstraction. The higher concentrations were predicted for 2-4 D and Glyphosates. For risk ranking, a toxicity score is proposed calculated as the peak concentration divided by a Reference Dose. The pesticide Methamidofos was found to account for more than 93,7% of the total risk, followed by 2-4 D with 1,7%, Dimethoate, MCPA, and Paraquat with 0,8-0,9%. The pesticide Trifluralin was kept in the list as the only carcinogenic substance, although its risk quotient was very small. The average annual concentration of the most toxic pesticides according to the previous classification were estimated taking also into account the decay of pesticide in soil and in Lake water. Ignoring other exposure routes, i.e. consumption of vegetable products contaminated with pesticides or skin contact of farmers during pesticide application and taking into account only long-term life exposure due to drinking water consumption from the water of Lake Taka, it was found that the cumulative risk to human health was non significant. The methodology presented in this paper can serve as a rapid tool for Tier I assessment of ecological and human health risks from pesticides used in agriculture.