Chemical fate in the environment Molecular interactions (physical-chemical properties, reactivities) Environmental factors (Temperature, pH, light intensity, ion composition and strength, microbial activity, natural organic matter, etc.) Environmental processes (e.g. air/water exchange, sorption/desorption, chemical, photochemical and biological transformation)
Oregon State University Chemical fate in the environment Transport and mixing processes Dynamic behavior in a natural system (mathematical models and field investigations)
Oregon State University Chemicals in the Environment Initial distribution to environment (manufacture and use): emission in: air-soil-water-biota compartments Transformation: degradation/metabolism Redistribution- transport in and between compartments: diffusion/advection-dispersion/mass transport
Oregon State University Chemicals in the Environment Understanding chemical fate, what scale? Local scale: site-specific inputs, potential for off-site transport. Watershed scale: integration of site-specific inputs and transport, particular emphasis on water quality. Regional scale: integration of watershed- airshed chemical inputs and redistribution, long range transport of persistent compounds.
Oregon State University Range of ESA Listed Salmon
Oregon State University Pesticides in the Environment Initial distribution in the environment: method of application timing of application frequency of application amount of active ingredient formulation (other ingredients)
Oregon State University Environmental Behavior of Pesticides in Soils Initial distribution Persistence and Mobility Environmental Fate temperature soil pH soil texture sunlight organic matter moisture
Oregon State University Pesticide Fate and Transport Physical-chemical properties: Water solubility Vapor Pressure Kd (soil/water partition coefficient) Henrys Law Constant Soil half-life Foliar half-life
Course textured soils and other soil conditions that result in preferential flow paths must also be considered.
Oregon State University Pesticides in Ground and Surface Water
Oregon State University Pesticides in surface water Mass transfer primarily in the dissolved phase, will vary with pesticide’s solubility in water and soil sorption. soil particle water concentration of pesticide sorbed to soil concentration of pesticide in solution
Oregon State University Partitioning between soil compartments (soil, water air)
Oregon State University Pesticide Fate Field dissipation: sum of chemical and biological processes including: –Chemical degradation 1 –Biological degradation (microbial + plant) 1 –Photodegradation 2 –Volatilization 1 Approximated with a 1 st order rate constant 2 Approximated with a psuedo 1 st order rate constant
Oregon State University Pesticide degradation half-life Half-life = the amount of time it takes the parent compound to decay to half its original amount Half-life in an environmental compartment: (soil-air-water-biota) sum of all degradation and transport pathways
Oregon State University Pesticide degradation half-life No of ½ lives % amount remaining 3.310 6.61 100.1
Oregon State University Sunlight photolysis of an aqueous suspension of nitrofen
Oregon State University Chemical and microbial degradation of chloroanilines
Oregon State University NOAEL LD 50 : lethal dose for ½ the test animals
Oregon State University Aldicarb degradation pathways and LD 50 values (rat acute oral)
Oregon State University Pesticide Properties used to evaluate fate in the Environment water sol ppm Koc ml/g Vapor pressure mm Hg soil 1/2 life days foliar 1/2 life days Atrazine331002.90E-07605 Diuron424806.90E-089030 MCPA ester510001.50E-06258 pendimethalin2850009.40E-069030 triclopyr ester237801.26E-064615 carbaryl1203001.20E-06107 chlorpyrifos0.460701.70E-05303 malathion13018008.00E-0613 esfenvalerate0.00253001.10E-08358
Oregon State University Chemical fate determines exposure to humans and aquatic life
Oregon State University 13.4 million lbs of pesticides used annually in Oregon What are the risks and who decides? Federal Insecticide, Fungicide, and Rodenticide Act regulates pesticide manufacture, use, storage, and disposal (benefit-risk balancing statute.) Under Authority of the Clean Water Act, ODEQ has the authority to set pesticide water quality standards for waters of the state (TMDLs). Under the Endangered Species Act NMFS and USFWS have the authority to set rules deemed necessary to prevent more species declines under a provision called “Four D.” EPA, NMFS, and USFWS have “overlapping” jurisdiction with regards to pesticide use and the Endangered Species Act.
Oregon State University EPA Risk Assessment Risk = f (exposure, toxicity) Source: Purdue University Pesticides Program
Oregon State University Pesticide Risk Assessment RFD: The Reference Dose is the amount of a pesticide residue a person could consume daily for 70 years with no harmful non-cancer effects.
Oregon State University Pesticide Risk Assessment The RFD is determined by dividing the NOAEL by a safety factor, usually between 100 and 1000, to account for uncertainty in extrapolating from animal studies and to protect sensitive individuals, including infants and children.
Oregon State University Quantitative Assessment of Health Risks of Pesticides in Drinking Water MCL - The Maximum Contaminant Level permissible in water which is delivered to any user of a public water system (Safe Drinking Water Act; ~50 pesticides have MCLs) HA - Health Advisory: EPA guidance for drinking water contaminants based on lifetime exposure and non- carcinogenic endpoints. HA is derived from the DWEL. DWEL - Drinking Water Equivalent Level, based on the Reference Dose (RfD) and assuming 70 Kg person drinks 2 liters per day over a lifetime. The DWEL has been adjusted assuming that drinking water comprises 20% of the allowable daily intake.
Oregon State University Pesticide Risk Assessment: Wildlife What is the toxicity of the pesticide and it’s degradates to wildlife? Acute toxicity (high dose-short exposure) Chronic toxicity (low dose-long exposure) Most sensitive adverse effect Sensitive sentinel species
Oregon State University EPA Pesticide Aquatic Risk: Wildlife Toxicity Assessment Laboratory tests are used to determine the NOAEL in representative species. The hazard quotient is the ratio of the NOAEL to the expected environmental concentration. If the hazard quotient is greater than 1.0, the potential exists for adverse ecological effects.
Oregon State University Use of models for evaluating hazards associated with chemicals in the environment Models use a systems approach to understanding complex phenomenon. Computer based environmental models present a conceptual framework and a mathematical formulation of fate and transport between compartments (soil, air, water, biota) based upon scientific principles.
Oregon State University Environmental fate models PRZM and EXAMS (EPA) CalTOX (California EPA) Fugacity Model Levels I, II, III (Mackay) Gaussian plume models (EPA, NOAA) http://www.lanl.gov/orgs/d/d4/movies.shtml
Oregon State University Fugacity Model for Biphenyl
Oregon State University Fugacity Model for Biphenyl
Oregon State University How Do We Assess Risk? Follow the National Academy of Sciences (NAS) four-step risk assessment paradigm*: * From the National Research Council’s Risk Assessment in the Federal Government: Managing the Process, 1983. Hazard Identification Risk Characterization Exposure Dose- Response Assessment