A Simple Model of Alachlor Dissipation

Abstract

Alachlor [2‐chloro‐N‐(2,6‐diethylphenyl)‐N‐(methoxymethyl) acetamide] dissipation in the field shows two characteristics: (i) rapid, initial loss followed by slower degradation and (ii) sensitivity to environmental conditions including precipitation patterns, soil temperature, and soil‐water content. Empirical models, such as a first‐order equation, are simple and easy to use, but they do not accurately predict alachlor dissipation in the field. Complex mechanistic models provide theoretical mechanisms for dissipation, but their usefulness can be limited because they typically require data that is difficult to acquire under field conditions. We developed a hybrid model (M2CM) for alachlor dissipation based on a two‐compartment model (2CM). Our model requires only easily‐collected weather, soil, and pesticide information. It predicts the daily amount of alachlor in the soil and calculates times for 50 and 90% dissipation. We calibrated it with data from 30‐cm‐deep field‐soil samples and weather records from the 1993 growing season. Using 1992 and 1994 environmental data, the model calculated dissipation values that fit field‐sample data accurately (0.95 ≤ r2 ≤ 0.99). Results from the 2CM were not as consistently satisfactory (0.64 ≤ r2 ≤ 0.97). According to the M2CM, the alachlor half‐life (time to 50% dissipation) was 1 d for all 3 yr. Time to 90% dissipation was 18 d for 1992, 23 d for 1993, and 15 d for 1994.

Occurrence and Fate of Pharmaceuticals and Personal Care Products (PPCPs) in Biosolids

“…The safest approach to avoid potential detrimental effects of biosolids‐associated PPCPs to the environment is to ensure that the compounds are adequately degraded before biosolids land application. Composting has been used as an effective means to degrade xenobiotic organic contaminants such as pesticides, polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), trinitrotoluene (TNT), and perchlorate (Williams and Keehan, 1993; Rao et al, 1995; Wallace et al, 1998; Büyüksönmez et al, 1999; Weed et al, 1999). Composting may accelerate the degradation of organic contaminants due to their exposure to high microbial diversity and activity (especially thermophilic organisms), abundant substrates, high temperature, changing pH, and successive shifts in aerobic and anaerobic conditions in microenvironments within a composting system (Büyüksönmez et al, 1999; Barker and Bryson, 2002).…”

Bioremediation of contaminated soil and sediment by composting

“…The bulky structures of the organic material in compost open and stabilize the structure of contaminated soil in most cases (Laine et al, 1997). Secondary enhancers of microbial activity include moisture, inorganic nutrients, and oxygen.The nature of the organic contaminant, composting conditions and procedures, microbial communities, and time all affect mechanisms or conversions in composts or soils (Weed et al, 1999).…”

Nonpoint Sources

“…A new model was introduced which uses relatively available data and empirically derived coefficients to determine alachlor dissipation (Weed et al, 1999). The twocompartment model was calibrated on one year of field study data and then tested against two other years, which it simulated relatively closely.…”