Distribution of Dissolved Pesticides and Other Water Quality Constituents in Small Streams, and their Relation to Land Use, Willamette River Basin, Oregon

Water quality samples were collected at sites in 16 randomly selected agricultural and 4 urban subbasins as part of Phase III of the Willamette River Basin Water Quality Study in Oregon during 1996. Ninety-five samples were collected and analyzed for suspended sediment, conventional constituents (temperature, dissolved oxygen, pH, specific conductance, nutrients, biochemical oxygen demand, and bacteria) and a suite of 86 dissolved pesticides. The data were collected to characterize the distribution of dissolved pesticide concentrations in small streams (drainage areas 2.6? 13 square miles) throughout the basin, to document exceedances of water quality standards and guidelines, and to identify the relative importance of several upstream land use categories (urban, agricultural, percent agricultural land, percent of land in grass seed crops, crop diversity) and seasonality in affecting these distributions. A total of 36 pesticides (29 herbicides and 7 insecticides) were detected basinwide. The five most frequently detected compounds were the herbicides atrazine (99% of samples), desethylatrazine (93%), simazine (85%), metolachlor (85%), and diuron (73%). Fifteen compounds were detected in 12?35% of samples, and 16 compounds were detected in 1?9% of samples. Water quality standards or criteria were exceeded more frequently for conventional constituents than for pesticides. State of Oregon water quality standards were exceeded at all but one site for the indicator bacteria E. coli, 3 sites for nitrate, 10 sites for water temperature, 4 sites for dissolved oxygen, and 1 site for pH. Pesticide concentrations, which were usually less than 1 part per billion, exceeded State of Oregon or U.S. Environmental Protection Agency aquatic life toxicity criteria only for chlorpyrifos, in three samples from one site; such criteria have been established for only two other detected pesticides. However, a large number of unusually high concentrations (1?90 parts per billion) were detected, indicating that pesticides in the runoff sampled in these small streams were more highly concentrated than in the larger streams sampled in previous studies. These pulses could have had short term toxicological implications for the affected streams; however, additional toxicological assessment of the detected pesticides was limited because of a lack of available information on the response of aquatic life to the observed pesticide concentrations. Six pesticides, including atrazine, diuron, and metolachlor, had significantly higher (p<0.08 for metolachlor, p<0.05 for the other five) median concentrations at agricultural sites than at urban sites. Five other compounds ?carbaryl, diazinon, dichlobenil, prometon, and tebuthiuron?had significantly higher (p<0.05) concentrations at the urban sites than at the agricultural sites. Atrazine, metolachlor, and diuron also had significantly higher median concentrations at southern agricultural sites (dominated by grass seed crops) than northern agricultural sites. Other compounds that had higher median concentrations in the south included 2,4-D and metribuzin, which are both used on grass seed crops, and triclopyr, bromacil, and pronamide. A cluster analysis of the data grouped sites according to their pesticide detections in a manner that was almost identical to a grouping made solely on the basis of their upstream land use patterns (urban, agricultural, crop diversity, percentage of basin in agricultural production). In this way inferences about pesticide associations with different land uses could be drawn, illustrating the strength of these broad land use categories in determining the types of pesticides that can be expected to occur. Among the associations observed were pesticides that occurred at a group of agricultural sites, but which have primarily noncropland uses such as vegetation control along rights-of-way. Also, the amount of forested land in a basin was negatively associated with pesticide occurrence

1996年，作为俄勒冈州威拉米特河流域（Willamette River Basin）水质研究第三阶段的一部分，研究人员在随机选取的16个农业子流域与4个城市子流域的采样点位采集了水质样本。本次共获取95份样本，针对悬浮沉积物（suspended sediment）、常规水质参数（温度、溶解氧（dissolved oxygen）、pH、比电导率（specific conductance）、营养盐（nutrients）、生化需氧量（biochemical oxygen demand）与细菌类）以及86种溶解态农药开展了检测分析。本数据集的采集旨在刻画全流域小型溪流（汇水面积2.6~13平方英里）内溶解态农药浓度的分布特征，记录水质标准与指南的超标情况，并明确上游多种土地利用类型（城市用地、农业用地、农业用地占比、草籽作物用地占比、作物多样性）与季节变化对上述分布的相对影响程度。全流域共检出36种农药（含29种除草剂（herbicides）与7种杀虫剂（insecticides））。检出频率最高的五种化合物均为除草剂：阿特拉津（atrazine，检出率99%）、脱乙基阿特拉津（desethylatrazine，93%）、西玛津（simazine，85%）、甲草胺（metolachlor，85%）与敌草隆（diuron，73%）。另有15种化合物的检出率介于12%~35%，16种化合物的检出率为1%~9%。常规水质参数的超标频率高于农药类化合物。俄勒冈州水质标准的超标情况如下：指示菌大肠杆菌（E. coli）的超标点位除1处外全部覆盖，硝酸盐超标点位共3处，水温超标点位10处，溶解氧超标点位4处，pH超标点位1处。农药浓度通常低于1十亿分之一（part per billion，ppb），仅在某点位的3份样本中，毒死蜱（chlorpyrifos）的浓度超过了俄勒冈州或美国环境保护署（U.S. Environmental Protection Agency）的水生生物毒性标准；目前仅针对另外2种检出农药制定了此类标准。不过本次研究仍检出大量浓度异常偏高的样本（浓度区间为1~90 ppb），表明这些小型溪流径流中的农药浓度高于此前研究中大型溪流的检测结果。此类浓度脉冲可能对受影响的溪流造成短期生态毒性影响，但由于缺乏水生生物对本次检测到的农药浓度的响应相关数据，针对检出农药的进一步生态毒性评估受到了限制。共有6种农药（包括阿特拉津、敌草隆与甲草胺）在农业点位的浓度中值显著高于城市点位（甲草胺的显著性水平p<0.08，其余5种均为p<0.05）。另有5种化合物：西维因（carbaryl）、二嗪农（diazinon）、敌草腈（dichlobenil）、扑灭通（prometon）与噻苯隆（tebuthiuron），在城市点位的浓度显著高于农业点位（p<0.05）。阿特拉津、甲草胺与敌草隆在南部农业点位（以草籽作物种植为主）的浓度中值同样显著高于北部农业点位。其余在南部点位浓度中值更高的化合物包括均用于草籽作物种植的2,4-滴（2,4-D）与嗪草酮（metribuzin），以及三氯吡氧乙酸（triclopyr）、溴谷隆（bromacil）与普罗帕胺（pronamide）。对数据集开展聚类分析后，点位的分组结果与其基于农药检出情况的分组结果高度一致，与仅根据上游土地利用类型（城市用地、农业用地、作物多样性、流域农业生产占比）划分的分组结果几乎完全重合。借此可推断农药检出情况与不同土地利用类型之间的关联，表明此类宽泛的土地利用类型分类可有效预判流域内可能出现的农药类型。本次研究观测到的关联包括：部分农药仅在农业点位检出，但这类农药的主要用途并非农田种植，而是用于沿线植被防控等非农田场景。此外，流域内林地占比与农药检出情况呈负相关关系。