Bioaccumulation of trace metals and their biochemical influence on the tissues of clam Ruditapes philippinarum

Abstract

해양 퇴적물은 금속의 저장 장소로 생태계에서의 해결책 역할 뿐만 아니라 대부분 오염의 최종 저장소이며, 이러한 금속은 강을 통해 해양으로 유입되고 있다. 패류는 풍부하게 분포하고 있으며 바다에서 서식하는 이유로 세계적으로 지표생물로 이용되어 왔다. 이러한 패류 중 바지락은 우리나라 연안에 널리 분포하고 있으며 금속 오염의 생체지표로 적당할 수 있다. 카드뮴은 해양 환경에 널리 분포하고 있으며 생물체에서 독성을 일으키는 주요 오염물질이다. 납은 비 필수 금속으로 해양 생태계에서 많은 다른 금속 오염보다 더 낮은 농도에서 독성 영향이 미칠 수 있다. 그러므로 이번 연구의 목적은 (a) 바지락 양식장에서의 해수, 퇴적물, 바지락의 금속 농도를 평가하고 (b) 카드뮴과 납 노출에 따른 바지락에서의 항산화 효소의 활성으로 카드뮴과 납의 축적과 제거를 설명하는 것이 목적이다. 바지락 양식장에서 해수, 퇴적물과 바지락의 금속 (Cu, Cd, Pb, Cr, As, Se, Zn)을 측정하였다. 진해 지역의 바지락 양식장에서 해수 농도에서 구리, 납, 아연이 가장 높았다. 구리에서는 2.40 ？ 0.69 ㎍/L, 납에서는 2.07 ？ 0.48 ㎍/L, 아연에서는 6.83 ？ 1.65 ㎍/L으로 나타났다. 비소는 사천지역에서 가장 높은 값 5.42 ？ 5.55 ㎍/L로 나타났다. 카드뮴과 크롬, 셀레늄은 모든 양식장에서 비슷한 값을 보였다. 전체적으로 고흥 지역의 바지락 양식장 해수에서 가장 낮은 금속 농도가 조사되었다. 진해 지역의 양식장 퇴적물 구리 농도는 44.15 ~ 50.05 ㎍/g으로 나타나 가장 높은 농도를 보였으며, 카드뮴, 납과 아연도 다른 지역의 농도보다 높았다. 그러나 크롬은 고흥 지역의 퇴적물에서 가장 높은 농도로 나타났다. 결과적으로 크롬을 제외한 퇴적물 내 금속 농도는 진해 지역에서 가장 높게 조사되었다. 모든 조사 지역의 바지락 조직 내 구리, 크롬, 비소, 셀레늄, 아연 농도가 아가미에서 다른 조직보다 높았으며, 바지락 조직에서의 금속 농도는 고흥 지역에서 가장 낮게 조사되었다. 카드뮴 및 납에 대한 실내 노출실험 결과, 카드뮴 축적은 노출 시간에 따라 증가하였으며, 배출은 100 ppb 이하의 농도에서 감소되는 양상으로 나타났다. 2주 동안 카드뮴 축적의 조직 순서는 아가미 > 소화선 > 나머지 조직으로 나타났으며, 배출 기간에서 200 ppb를 제외한 농도에서 감소되는 카드뮴 농도로 나타나고 있으며, 배출 순서는 소화선 > 아가미 > 나머지 조직 순으로 나타난다. SOD, GST, GR, GSH, MDA 활성은 200 ppb 농도 구에서 증가된 유의성이 나타난다. GPx 활성에서 200 ppb에서 감소한 유의성이 나타나고 있다. 납 축적 실험에서의 납 축적은 시간에 따라 증가되고 150 ppb 이상에서 축적되고 배출 시에도 150 ppb 농도 구에서 제거가 이루어지고 있다. 2주 동안의 납 노출 기간 동안 조직에서의 납 축적 순서는 아가미 > 나머지 조직 > 소화선으로 나타나며, 배출 기간에서의 납 농도는 증가된 150 ppb 이상의 농도 구에서 즉각적인 제거가 이루어지고 있으며, 납 제거 순서는 아가미 > 소화선 > 나머지 조직으로 나타난다. SOD, GPx, GSH 활성은 150 ppb 이상의 농도에서 유의성이 나타나고 있다. GR 활성은 300 ppb 농도에서 유의성이 나타나며, GST 활성에서 300 ppb에서 증가된 유의성이 나타난다. MDA 변화에서 30 ppb 이상에서 유의성이 나타나고 있다. 결론적으로 연안에 존재하는 중금속 오염 평가를 위한 상기의 바지락의 중금속 축적 및 생물반응의 결과는 연안의 오염 평가를 위해 부분적으로 적용될 수 있으며, 특히 생물반응 결과는 위해성 평가에 적용될 수 있을 것으로 생각된다.

Marine sediments represent the final repository of most contaminants and elements carried to the oceans by rivers, but also play a key role in estuarine systems as potential sources and sinks for these substances. Clams have been selected as indicator organisms world wide because of their abundance, ubiquity, long life span, high filtration rate, and especially, because of concern in the sea. The clam Ruditapes philippinarum was a proposed as suitable biomonitors of metal contamination because of their wide distribution throughout in Korean costal regions. Cadmium was one of the major contaminants that was toxic to living organisms and was widely distributed in the marine environment. Lead was exerts toxic effects at lower concentrations than many other metallic contaminants. Therefore, the aims of the present study are (a) to evaluate the concentration of trace metal in seawater, sediment and clam at different clam-farm sites and (b) to investigate accumulated tissues and the effect of Cd and Pb exposure on the activities of protective antioxidant enzymes in the gill and digestive glands of the clam, R. pillippinarum in order to explain accumulation and elimination Cd and Pb in tissues. Concentrations of trace metals (Cu, Cd, Pb, Cr, As, Se, Zn) determined in different clam farms seawater, sediment and clams. Each metal concentration, Cu, Pb, Zn, were appeared to be the highest the clam farm of Jinhae. For Cu, the mean value was recorded at 2.40 ？ 0.69 ？g/L and Pb of mean value was at 2.07 ？ 0.48 ？g/L. Zn of mean value concentration was at 6.83 ？ 1.65 ？g/L. The highest As of mean value concentrations measured in Sacheon clam farm. This mean value was 5.42 ？ 5.55 ？g/L. Cd, Cr , Se mean values concentrations were similarity in all clam farms. As a whole, trace metal concentrations in seawater of Goheung clam farm were observed lower than the other clam farm. The concentrations of Cu range between 44.15 ？g/g and 50.05 ？g/g in the Jinhae clam farm, while the range 28.07 ~ 37.84 ？g/g and 18.78 ~ 29.04 ？g/g in the Sacheon, Goheung clam farm, respectively. The highest concentration of Cd (0.31 ？ 0.03 ？g/g dry wt.) was found at Jinhae clam farm. Pb was quite high (59.11 ~ 73.08 ？g/g dry wt.) in the sediment clam farm of Jinhae. The highest concentrations of Cr range between 82.00 and 85.69 ？g/g dry wt. in the Goheung clam farm. The concentrations Zn were very high (191.76 ~ 235.72 ？g/g dry wt.) in the sediment clam farm of Jinhae. As a result, all trace metals concentrations of sediment except Cr were the highest the clam farm of Jinhae. Cu, Cr, As, Se, Zn concentrations in gill was higher than other tissues at all sampling site. The highest Cr concentrations in clam tissues were recorded 2.18 ？ 1.80 ？g/g, 2.00 ？ 0.86 ？g/g in gill at Jinhae and Sacheon, respectively. The highest As, Se concentrations in clam gill tissues were recorded for Sacheon (73.40 ？ 12.91 As ？g/g, 7.62 ？ 1.89 Se ？g/g) clam farm. The highest Zn concentrations in clam tissues were recorded for Jinhae (e. g. 114.24 ？ 13.65 ？g/g in gill) clam farm. In conclusion, trace metal concentrations in clam tissues of Goheung clam farm were observed lower than the other clam farm and were recorded highest trace metals concentrations of gill in the clam tissues. Cd accumulation and depuration were assessed in the tissues of R. philippinarum in four experimental concentration (10, 20, 100, 200 μg/L) over eliminated period 1 week after exposed periods 2 weeks. Cd accumulated in the digestive glands, gills and residue tissues of the clam and the accumulation increased with the time of exposure (2 weeks) and concentration (over 100 μg/L), and the depuration decreased with below 100 μg/L concentration. At 2 weeks of Cd exposure, the order of Cd accumulation in tissues was gill > digestive glands > residue tissues. An inverse relationship was observed between the accumulation factors (AF) and the exposure level, but AF showed an increase with exposure time. During the depuration periods, Cd concentration in digestive glands, gill and residue tissues decreased immediately following the end of the exposure periods except 200 μg/L concentration. The order of Cd elimination rate in tissues were decreased digestive glands > gill > residue tissues during depuration periods. SOD activity no significant differences in the digestive glands of the clam observed during total periods. And gill only significantly deceased at 200 μg/L concentration in 2 weeks. GPx activity was observed at 200 μg/L concentration in 2 week decreased significant in the digestive glands and observed over 100 μg/L concentration in 2 week decreased significant in the gill. GR activity significantly increased at 200 μg/L concentration for total periods in the gill, but no activity observed in the digestive glands. GST activity significantly increased over 100 μg/L concentration for 1 week in the gill, and no observed after 2, 3 weeks. The digestive glands were observed significant increased at 200 μg/L concentrations in 1 week, significant decreased at 200 μg/L concentration in 2, 3 week. GSH activity was observed significantly increased at 200 μg/L concentration in total periods in the digestive gland. In the gill, GSH activities were increased at 200 μg/L Cd exposure group during 1 week, and then significantly increased at the 100 and 200 μg/L Cd concentrations in 2 week. But, it was significantly decreased at 200 μg/L Cd concentration during the depuration period. In digestive gland and gill, Malondialdehyde activity of Cd exposed to clams were significantly increased at the 200 μg/L, and then were no significant difference each Cd concentration in 2, 3 week Pb accumulation and depuration were assessed in the tissues of R. philippinarum in four experimental concentration (15, 30, 150, 300 μg/L) over eliminated period 1 week after exposed periods 2 weeks. Pb accumulated in the digestive glands, gills and residue tissues of the clam and the accumulation increased with the time of exposure (2 weeks) and concentration (over 150 μg/L), and the depuration decreased with above 150 μg/L concentration. At 2 weeks of Pb exposure, the order of Pb accumulation in tissues was gill > residue tissues > digestive glands. A direct proportion relationship was observed between the accumulation factor and the exposure concentrations at 1 week. Moreover the accumulation factor in over 150 μg/L increased with 2 week. During the depuration periods, Pb concentration in digestive glands, gill and other tissues decreased immediately following the end of the exposure periods above 150 and 300 μg/L concentrations. The order of Pb elimination rate in tissues were decreased digestive gill > digestive gland > residue tissues during depuration periods. SOD activity significantly decreased at 150 and 300 μg/L concentration in 2 week in the digestive gland, but no significantly decreased for depuration period. And gill showed decreasing level after 3weeks (150 and 300 μg/L). Malondialdehyde activity of gill and digestive gland showed decreasing level after 2weeks and 3weeks (300 μg/L). Glutathione activities in digestive gland and gill were decreased for all experimental periods at 150 and 300 μg/L. Glutathione peroxidase activities were decreased all experimental concentrations except 15 μg/L at 2weeks. Glutathione S-transferase activity which is protecting against oxygen toxicity was increased in 300 μg/L at 2 weeks. Glutathione reductase activity in gill was elevated 150 and 300 μg/L at 1 week. In conclusion, R. philippinarum can be considered a good bioindicator for Cd and Pb exposure. Antioxidant enzyme activity in the digestive glands and gill can be considered a potential biomarker of sub-lethal stress as a result of exposure to cadmium and lead. The choice of the tissues for determining the effect of trace metals also has advantages from the experimental point of view, because a smaller number of specimens will be necessary for analyzing enzyme activity. Although direct metal-enzyme interaction in the case of Cd and Pb cannot be eliminated as a possibility, the most probable cause of the response measured in this study is adaptive reaction to stress. Nevertheless, experiments carried out at environmentally relevant concentrations and field samples will be necessary to confirm the usefulness of antioxidant enzyme as a biomarker of stress by trace metal.