Comparative toxicity of single and combined mixtures of selected pollutants among larval stages of the native freshwater mussels (Unio elongatulus) and the invasive zebra mussel (Dreissena polymorpha).

This study evaluated the impact of biocides (tributyltin, chlorthalonil and Irgarol 1051) and of pollutants (copper, inorganic and methyl mercury and 4-nonylphenol) occurring in Ebro River (NE Spain) on early developmental stages of native Spanish freshwater and invasive zebra mussels. Toxicity tests were conducted with embryos and glochidia of zebra mussel (Dreissena polymorpha) and the naiad species Unio elongatulus, respectively. Toxicity was quantified in terms of median effective concentration (EC50) impairing embryogenesis and glochidia viability in single and combined mixture exposures. Irgarol 1051 was not toxic at concentrations below 40x10(3)nM. Zebra mussel embryos were on average 50 fold more sensitive to the studied pollutants than glochidia. Tributyltin was the most toxic compound with EC50s for zebra mussel embryos and glochidia, respectively, of 1.24 and 47.93 nM, followed by chlorothalonil (3.65, 176.58 nM), methyl mercury (7.06, 156.4 nM), inorganic mercury (3.64, 518.28 nM), copper (19.73, 1358.55 nM) and 4-nonylphenol (33.99, 1221.48 nM). Combined toxicity of Ebro River pollutants (copper, inorganic and methyl mercury and 4-nonylphenol) was greater than additive in zebra mussel embryos and additive in glochidia. These results indicated that contaminant levels that affect zebra mussel embryos are not toxic to early life stages of the naiad mussel species U. elongatulus.

DDT polluted meltwater affects reproduction in the mussel Dreissena polymorpha.

The zebra mussel Dreissena polymorpha was used to follow the recently reported DDT pollution of Lake Iseo (N. Italy). Histopathological analyses were performed on mussels sampled from March 2005 to April 2006, when high DDT levels were found, and results were compared to those from mussels sampled in 2001/2002, before the pollution event. During the 2005/2006 reproductive season, the first male gamete release happened one month later than the onset of spawning in females who showed a high number of specimens with degenerating oocytes, despite a regular pattern of gametogenesis. These results indicated a disrupting action of DDT on the mechanisms involved in sperm release, and a disturbance in the gametogenic phases of the ovary. Pathological pictures in the digestive gland of many mussels from both 2001/2002 and 2005/2006 have also been observed, but DDT pollution is unable to explain the presence of pathological fields in mussels during 2001/2002, for which a previously reported contamination seems to be the main cause. A possible role of DDT in skewing the sex ratio towards a predominance of females was also discussed, considering the high number of females sampled in 2005/2006.