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Efeitos da acumulaçäo de chumbo em pós-larvas de ameijoa-boa (Ruditapes decussatus L.)
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Advisor(s)
Abstract(s)
O objectivo deste estudo consistiu em estudar os efeitos da acumulação do chumbo (sob a forma de nitrato) em pós-larvas de ameijoa-boa (Ruditapes decussatus).
Os animais sofreram exposição crónica ao chumbo no meio de cultivo a concentrações elevadas durante 90 dias com 200 e 400 ug Pb/l e com baixas concentrações, 50 e 100 ug Pb/l durante 30 dias.
Demonstrou-se que o crescimento foi afectado negativamente pelo chumbo mas não foi proporcional à quantidade de metal adicionado na água.
No entanto, a razão de RNA/DNA não apresentou alterações entre os animais de controlo e os em meio com chumbo.
Estudou-se duas vias de contaminação com chumbo: no meio de cultivo e através do alimento. Verificou-se que os animais acumularam chumbo pelas duas vias.
Contaminaram-se as pós-larvas com chumbo por períodos de tempo diferentes verificando-se que os efeitos negativos no crescimento são independentes do período de exposição. Os animais em meio contaminado acumularam o poluente até um certo ponto, o que sugere a existência de um mecanismo de regulação da concentração do chumbo no seu interior, para esta espécie. Quando transferidos para água limpa eliminaram o chumbo muito rapidamente.
De modo a eliminar a possibilidade dos nitratos (do Pb(NO3)2) causarem um efeito negativo no crescimento foi estudado o seu efeito no crescimento. Os resultados demonstraram que não há influência no crescimento.
The objective of this study was to investigate the effects of accumulation of lead (as lead nitrate) in post-larvae of Ruditapes decussatus. The animals were Subject to chronic exposure to high concentrations of lead during 90 days with 200 and 400 ug Pb/l and to low concentrations, 50 and 100 ug Pb/l during 30 days, in seawater. The results demonstrated that growth was affected negatively by lead and this relationship was not linear with the concentration of lead in seawater. However, using RNA/DNA ratios no differences were observed between treated and control animals. Two ways of adininistering lead were considered; addition to seawater or addition to food. Lead accumulation was measured in homogenates by atomic absorption. It was demonstrated that the animals accumulated lead by both routes of administration. The animals were contaminated with lead for different periods of time. The negative effects on growth were independent of the period of exposure. Regardless of the time of exposure to lead, animals all appeared to accumulate it until a certain concentration after which levels were maintained and no further increase occurred. This suggests that a regulatory mechanism for lead may exist in this species. When transferred to clean seawater the lead was eliminated very quickly. In order to eliminate the possibility that nitrates (from Pb(NO3)2) caused the negative growth effect observed, the effect of nitrate on growth was studied in the experiments. The results of this study showed nitrates did not influence growth.
The objective of this study was to investigate the effects of accumulation of lead (as lead nitrate) in post-larvae of Ruditapes decussatus. The animals were Subject to chronic exposure to high concentrations of lead during 90 days with 200 and 400 ug Pb/l and to low concentrations, 50 and 100 ug Pb/l during 30 days, in seawater. The results demonstrated that growth was affected negatively by lead and this relationship was not linear with the concentration of lead in seawater. However, using RNA/DNA ratios no differences were observed between treated and control animals. Two ways of adininistering lead were considered; addition to seawater or addition to food. Lead accumulation was measured in homogenates by atomic absorption. It was demonstrated that the animals accumulated lead by both routes of administration. The animals were contaminated with lead for different periods of time. The negative effects on growth were independent of the period of exposure. Regardless of the time of exposure to lead, animals all appeared to accumulate it until a certain concentration after which levels were maintained and no further increase occurred. This suggests that a regulatory mechanism for lead may exist in this species. When transferred to clean seawater the lead was eliminated very quickly. In order to eliminate the possibility that nitrates (from Pb(NO3)2) caused the negative growth effect observed, the effect of nitrate on growth was studied in the experiments. The results of this study showed nitrates did not influence growth.