Occurrence of neutral chloroacetamide herbicide degradates in natural waters and their removal during drinking water treatment

Although herbicides are frequently encountered in groundwater, surface water and drinking water, relatively little is known about the occurrence of herbicide degradates in natural waters. The chloroacetamides (alachlor, acetochlor, metolachlor and dimethenamid) are a class of agricultural herbicides that is widely used in the U.S. These herbicides are known to have adverse human health effects. Some neutral chloroacetamide degradates possess a toxicity similar to the parent herbicide and may be considered in future drinking water regulations. This research attempts to redress the lack of data concerning the occurrence of neutral chloroacetamide herbicide degradates and the fate of these degradates during drinking water treatment.; For this study, 20 neutral degradates of alachlor, acetochlor, metolachlor and dimethenamid were examined. A method for concentration of the parent herbicides and degradates was developed using solid phase extraction, and analyses were subsequently performed using gas chromatography/mass spectrometry (GC/MS) with large-volume injections (100 muL) that afforded detection limits in the hundreds of pg/L range (ng/L range for degradates possessing a hydroxy substituent).; Analysis of samples obtained from the upper Chesapeake Bay revealed many neutral degradates, some at concentrations up to ten times that of the parent herbicide. Total concentrations of neutral degradates exceeded the parent herbicides by a factor of 20 to 30. Raw and finished Midwestern U.S. drinking water samples also revealed the presence of many chloroacetamide degradates. Neutral degradates in raw drinking water were present at concentrations (∼10--100 ng/L) similar to the parent herbicide; their summed concentrations contributed a significant fraction to the total pesticide and degradate concentrations.; Studies of degradate behavior during simulated unit processes reveal that neutral chloroacetamide degradates are not efficiently removed upon coagulation/flocculation, and only those degradates that lacked an acetanilide functional group react readily with aqueous chlorine. All compounds studied underwent removal with ozone or activated carbon. Those degradates that are more water soluble than the parent would require higher carbon doses to achieve efficient removal. These bench scale findings support the general lack of removal encountered in comparing raw versus finished drinking water samples; only sites using activated carbon during spring (for control of atrazine) experienced appreciable removal.