Department of Geography and Environmental Engineering, Johns Hopkins University, 3400 North Charles Street, Baltimore, MD, 21218, USA,
Environ Sci Pollut Res Int. 2014 Mar;21(6):4453-60. doi: 10.1007/s11356-013-2403-5. Epub 2013 Dec 12.
Transformations of cocaine and eleven of its metabolites were investigated in untreated municipal sewage at pH ≈ 7 and 9, 23, and 31 °C. Results indicated that hydrolysis-possibly bacterially mediated-was the principal transformation pathway. Residues possessing alkyl esters were particularly susceptible to hydrolysis, with pseudo-first-order rate constants varying from 0.54 to 1.7 day(-1) at 23 °C. Metabolites lacking esters or possessing only a benzoyl ester appeared stable. Residues lacking alkyl esters did accumulate through hydrolysis of precursors, however. As noted previously, this may positively bias cocaine utilization estimates based on benzoylecgonine alone. Reported variability in metabolic excretion was used in conjunction with transformation data to evaluate different approaches for estimating cocaine loading. Results indicate that estimates derived from measurands that capture all major cocaine metabolites, such as COCtot (the sum of all measurable metabolites) and EChyd (the sum of all metabolites that can be hydrolyzed to ecgonine), may reduce uncertainty arising from variability in metabolite transformation and excretion, possibly to ≈ 10 % RSD. This is more than a two-fold reduction relative to estimates derived from benzoylecgonine (>26 % RSD), and roughly equivalent to reported uncertainties from sources that are not metabolite-specific (e.g., sampling frequency, flow variability). They and other composite measurands merit consideration from the sewage epidemiology community, beginning with efforts to evaluate the stability of the total cocaine load under realistic sewer conditions.
在 pH 值约为 7 和 9、23 和 31°C 的未经处理的城市污水中，研究了可卡因和其 11 种代谢物的转化。结果表明，水解（可能是由细菌介导的）是主要的转化途径。含有烷基酯的残留物特别容易水解，在 23°C 时，伪一级速率常数从 0.54 到 1.7 天(-1)不等。缺乏酯类或仅含有苯甲酰酯的代谢物则表现稳定。然而，缺乏烷基酯的残留物会通过前体的水解而积累。如前所述，这可能会使仅基于苯甲酰古柯碱的可卡因利用率估计产生正向偏差。代谢排泄的可变性与转化数据一起用于评估估算可卡因负荷的不同方法。结果表明，根据可测量的所有主要可卡因代谢物（如 COCtot（所有可测量代谢物的总和）和 EChyd（所有可水解为古柯碱的代谢物的总和））估算得到的结果，可能会降低因代谢物转化和排泄的可变性而产生的不确定性，其不确定性可能会降低到 10%左右的相对标准偏差。与基于苯甲酰古柯碱的估算结果（>26%的相对标准偏差）相比，这是一个两倍多的降低，大致相当于非代谢物特异性来源的报告不确定性（例如，采样频率、流量变化）。这些和其他复合测量值值得污水流行病学界的关注，首先要努力评估在实际污水条件下总可卡因负荷的稳定性。
