Comparing Acute and Swimming Endpoints to Evaluate the Response of Two Freshwater Midge Species, Chironomus yoshimatsui and Chironomus riparius to Heavy Metals

The relative sensitivity of two freshwater non- biting midges, Chironomus yoshimatsui Martin and Sublette and C. riparius Meigan, was examined for lead, cadmium, and mercury in water- only exposures. Two endpoints were compared to assess toxicity 48 h and 96 h after exposure: Acute toxicity ($50\%$ lethal concentration: $LC_50$) and behavioral toxicity ($50\%$ effective concentration: $EC_{50}$). for the behavioral toxicity, reduction of swimming performance of two midge species in the treated conditions was compared to that in the untreated control. The sensitivities differed depending on the species and heavy metals, although some trends emerged. $LC_50$ values in C. yoshimatsui to cadmium and lead were always higher than those in C. riparius with increasing toxicity, regardless of the exposure times. The opposit was true for the mercury treatment. Similar trends were observed in the $EC_{50}$ values. The $EC_{50}$ values were always lower than the $LC_50$ values in all the treatment cases (midge species, heavy metals, and exposure times). These results indicate that the two midge species respond to the heavy metals differently: C. riparius is sensive to cadmium and lead and C. yoshimatsui to mercury. Behavioral toxicity such as swimming performance can be an effective endpoint for assessing heavy metal toxicity in water.

요시마쯔깔따구와 리파리깔따구(파리목: 깔따구과)의 중금속에 대한 급성독성 및 유영능력 비교

한국산 요시마쯔깔따구(Chironomus yoshimatsui)의 세 가지 중금속(납, 카드뮴, 수은)에 대한 급성독성 및 행동 독성을 외국 표준 실험 종인 리파리깔따구(C. riparius)와 비교하였다 48시간 및 96시간 동안 수중 노출(water-only exposure)을 시킨 후 두 가지 실험종의 반수치사농도($LC_50$)및 깔따구의 유영 능력 감소에 영향을 주는 농도($EC_{50}$)를 바탕으로 두 실험 종간의 차이를 살펴보았다. 카드뮴과 납에 대하여는 요시마쯔깔따구가 리파리깔따구에 비해 둔감한 반응을 보였으며, 수은에 대하여는 요시마쯔깔따구가 더 민감한 반응을 나타냈다. 모든 실험에서 $LC_50$값과 $EC_{50}$값의 비율이 1보다 높게 나와 사망률보다는 유영 능력을 기준으로 실시한 급성독성 평가가 더욱 민감한 결과를 얻었다. 노출 기간에 따른 급성독성 차이를 살펴본 결과 노출 기간이 길수록 급성독성 및 행동독성도 높게 나타났다.