Zurawell Ronald W, Holmes Charles F B, Prepas Ellie E
Department of Biological Sciences, University of Alberta, Edmonton, Alberta.
J Toxicol Environ Health A. 2006 Feb;69(3-4):303-18. doi: 10.1080/15287390500227498.
It has been suggested that little to no microcystin (MC), a cyanobacterial hepatotoxin, accumulates within freshwater pulmonate snails because the toxin is associated primarily with undigested gut contents that are eliminated from the animal via egestion. To test this, Lymnaea stagnalis exposed to MC-containing cyanobacteria were placed into toxin-free environments and sampled over short (24 h at 21 degrees C) and long (30 d at 22 and 10 degrees C) time periods. Within 8 h after being removed from exposure to microcystin-containing phytoplankton, the gizzard and cecal string fractions of the feces were eliminated, accounting for 57% of the initial MC concentration. However, detectable concentrations remained beyond 24 h, likely in association with the digestive-gland contents, which can be retained up to 100 h. Long-term MC loss was biphasic at two ambient temperatures. The greatest change (fast phase) occurred over the first 3 d after exposure. By 6 d, the cumulative MC loss from L. stagnalis was 80 and 95% at 10 and 22 degrees C, respectively. Toxin loss over this period was attributed to egestion of indigestible cells/colonies from gizzard and cecum, as well as elimination of unassimilated MC-laden fragments and vacuolate excretion of residues from the digestive gland. The fast-phase depuration rate constant was significantly higher at 22 than at 10 degrees C, indicating an influence of ambient temperature on the rate of toxin loss from pulmonate snails. Depuration continued at slower rates until 30 d, when most (97.5 and 99.5% at 10 and 22 degrees C, respectively) of the initial MC was eliminated.
有人提出，淡水肺螺体内几乎不会积累微囊藻毒素（MC，一种蓝藻肝毒素），因为这种毒素主要与未消化的肠道内容物相关，而这些内容物会通过排遗从动物体内排出。为了验证这一点，将暴露于含MC蓝藻的椎实螺置于无毒环境中，并在短时间（21摄氏度下24小时）和长时间（22摄氏度和10摄氏度下30天）内进行采样。从暴露于含微囊藻毒素的浮游植物中移除后的8小时内，粪便的砂囊和盲肠串部分被排出，占初始MC浓度的57%。然而，24小时后仍可检测到浓度，这可能与消化腺内容物有关，消化腺内容物可保留长达100小时。在两个环境温度下，MC的长期损失呈双相性。最大的变化（快速阶段）发生在暴露后的前3天。到第6天，在10摄氏度和22摄氏度下，椎实螺累积的MC损失分别为80%和95%。这一时期的毒素损失归因于砂囊和盲肠中不可消化细胞/菌落的排遗，以及未同化的含MC片段的排出和消化腺中残留物的液泡排泄。快速阶段的净化速率常数在22摄氏度时显著高于10摄氏度，表明环境温度对肺螺毒素损失速率有影响。净化以较慢的速率持续到30天，此时初始MC的大部分（10摄氏度和22摄氏度下分别为97.5%和99.5%）被排出。
