Pesticide concentration changes

The pesticide concentrations in the soil and liquid samples taken from these pits showed extreme variations which necessitated collecting and compositing samples from many different points to estimate the average pesticide concentrations and their change with time. Water, soil and air samples were also collected and analyzed to evaluate the possible contamination of the surrounding environment. Summarized conclusions from these investigations are ... 

Table I presents the change in concentration of each pesticide as a function of time at the three initial levels of 20 mg/L, 60 mg/L and 100 mg/L. The theoretical pesticide concentration is also shown in Table I as calculated from Equation 4 with k = 1, which assumes complete pesticide removal in one pass. The data are graphed and presented in Figure 5 as tank concentration versus time.

Another technique is to monitor drug or toxicant excretion rather than blood concentrations, especially when blood or plasma concentrations are very low. Using the same equations, the AUC is now replaced by chemical concentrations in urine, feces, and expired air. Some chemicals are primarily excreted by the kidney and urine data alone may be necessary. The rate and extent of absorption are clearly important for therapeutic and toxicological considerations. For example, different formulations of the same pesticide can change the absorption rate in skin or gastrointestinal tract, and not bioavailability, but can result in blood concentrations near the toxic dose. Also different formulations can result in similar absorption rates but different bioavailability. 

The general ADD equation described above is applicable when intake rate, exposure duration, exposure frequency, body weight and pesticide concentration remain constant over the time period of interest. If they change over time, then it is necessary to use either a summation or integration approach to calculate potential dose (USEPA, 1992a). 

Regulation of permissible pesticide levels in food, water, air, and soil presents a special problem. A maximum permissible level (MPL) is set for each food that may contain a pesticide residue, according to the amount of that food consumed in daily nutrition. Pesticide concentrations that are less than the MPL will not change the food s palatability or nutritive value. Milk, berries (black currants, raspberries, and strawberries) and other products for children s and dietetic nutrition are forbidden to have pesticide residues. The acceptable daily intake (ADI) covers not only the foods that may contain residues but also allows for possible pesticide entry from water and air. For foods that under proper application methods will have residues that do not exceed the ADI, the MPL is set from actual conditions to permit a low level of pesticide content. The Instructions present examples of substantiated MPLs for foods, established on the basis of daily consumption rates and observed residues. 

Maximum allowable concentrations (MACs) for pesticides in water must take into account the effects on palatability and sanitary status. These data are compared with toxicological research to define an index of limits for use in establishing the MAC. If the organoleptic properties of water are affected by pesticide concentrations lower than those that produce threshold changes in tests on animals, palatability becomes the limiting index. If toxic alterations occur at concentrations that do not render the water unpalatable, the standard is set on the basis of toxicological criteria. Standards are established in a similar way for air. 

Herbert, B.M.J., Halsall, C.J., Villa, S., Jones, K.C., KaUenborn, R. 2005. Rapid changes in PCB and OC pesticide concentrations in Arctic snow. Environmental Science Technology 39, 2998-3005. 

There is a significant amount of data from other countries on the effects on human health of large-scale pesticide production and use, in particular of OPPs and OCPs. Even one-time, accidental contact with some OCPs and OPPs such as dieldrin, malathion, and parathion, can lead to changes in the encephalogram (which remain for a year after exposure), disruptions of sleep patterns and memory, loss of libido, and difficulties in concentration [3]. Global practice shows that all pesticides are toxic to humans. 

Preparation of a data bank of figures to establish trends, e.g. changes in pesticide residue concentration in foods with season, or from year to year. 

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