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VOL. 72 (3), 391-408, 2006 HARMFUL ALGAL BLOOMS, RED TIDES AND HUMAN...

suffering the symptoms and not through a screening (37). No human
mortalities to date have been reported from any cases of DSP
poisoning, although there has been considerable morbidity resulting
in hospitalisation (39).

OA AND CANCER

Cancer is an important problem in public health worldwide.
Colorectal cancer (CRC) is the second most frequent cause of death
from cancer in the more developed regions of the world (40). While
CRC mortality declined several years ago in most countries in the
European (from 1950 to 1990’s), mortality rates continues to increase
for Spain (41). Spain has experienced a mean yearly increase higher
in men (2.6%) than women (0,8%) since 1975, although there is a
tendency towards stabilization (42).

A considerable number of environmental influences (mainly
dietary factors) may play an important role in the development of
CRC (41,43-46). In addition to that, hereditary factors have been
observed in the aetiology of CRC (47).

OA can be a cancer-promoter. Numerous studies show that OK
induces morphological transformation of cells (48-49), and
micronucleus promoting (50). OA induce mutations and gene
deregulation at low concentrations (51). OA also has growth-
promoting effects on human cells (52-53). In addition, OA has been
reported to be a tumor promoter of cancer in animal models, mainly
related to skin, stomach and colon cancer (23, 54).

However, scarce works notice on real health-risk of consuming
DSP toxins (39). The DSP syndrome is most prevalent in Europe,
Japan and Chile, where aquaculture are extensively carried out (55).
The regular shellfish consumers are exposed to continuous uptake of
sub-acute levels of DSP toxins.

A HYPOTHESIS: OA AND COLORECTAL CANCER?

Several epidemiological studies associate CRC and dietary
practices (47, 56-57). We propose that the residual levels of DSP

401