Reliable delineation of aquatic toxicity cut-offs for poorly soluble hydrocarbons is lacking. In this study, vapor and passive dosing methods were applied in limit tests with algae and daphnids to evaluate the presence or absence of chronic effects at exposures corresponding to the water solubility for representative hydrocarbons from five structural classes: branched alkanes, mono, di, and polynaphthenic (cyclic) alkanes and monoaromatic naphthenic hydrocarbons (MANHs). Algal growth rate and daphnid immobilization, growth and reproduction served as the chronic endpoints investigated. Results indicated that the dosing methods applied were effective for maintaining mean measured exposure concentrations within a factor of two or higher of the measured water solubility of the substances investigated. Chronic effects were not observed for hydrocarbons with an aqueous solubility below approximately 5 μg/L. This solubility cut-off corresponds to structures consisting of 13-14 carbons for branched and cyclic alkanes and 16-18 carbons for MANHs. These data support reliable hazard and risk evaluation of hydrocarbon classes that comprise petroleum substances and the methods described have broad applicability for establishing empirical solubility cut-offs for other classes of hydrophobic substances. Future work is needed to understand the role of biotransformation in the observed presence or absence of toxicity in chronic tests.

缺乏对难溶碳氢化合物的水生毒性临界值的可靠描述。在这项研究中，在藻类和蚤类的极限测试中采用了蒸气和被动加药方法，以评估与五种结构类别的代表性碳氢化合物的水溶性相对应的暴露时是否存在慢性影响：支链烷烃，单，双和多环烷烃（环烷烃）和单环烷烃（MANH）。藻类生长速率和瑞香固定，生长和繁殖是研究的慢性终点。结果表明，所采用的剂量方法可有效地将测得的平均暴露浓度保持在所调查物质的测得的水溶性的两倍或更高。对于水溶性低于约5μg/ L的烃，未观察到慢性影响。该溶解度截止对应于由支链和环状烷烃的13-14个碳和MANHs的16-18个碳组成的结构。这些数据支持对包含石油物质的烃类进行可靠的危险和风险评估，并且所描述的方法对于确定其他类别的疏水性物质的经验溶解度临界值具有广泛的适用性。需要进一步的工作来了解生物转化在慢性试验中观察到的毒性存在与否中的作用。这些数据支持对包含石油物质的烃类进行可靠的危险和风险评估，并且所描述的方法对于确定其他类别的疏水性物质的经验溶解度临界值具有广泛的适用性。需要进一步的工作来了解生物转化在慢性试验中观察到的毒性存在与否中的作用。这些数据支持对包含石油物质的烃类进行可靠的危险和风险评估，并且所描述的方法对于确定其他类别的疏水性物质的经验溶解度临界值具有广泛的适用性。需要进一步的工作来了解生物转化在慢性试验中观察到的毒性存在与否中的作用。