In 2010 the Cawth
ron Institute adopted AOAC official method 2005.06 (Law
rence method) fo
r regulato
ry testing of pa
ralytic shellfish toxins. This included adapting the method to a UPLC fo
rmat and developing a
rapid pe
riodate sc
reen to eliminate the vast ma
jo
rity of samples with no PSTs p
resent. The method gained New Zealand
regulato
ry app
roval and has since been used to test >2000 samples. Soon afte
r implementation a ma
jo
r HAB of the toxic dinoflagellate
Alexandrium catenella occu
rred in a p
rime shellfish g
rowing a
rea of New Zealand. This event was the most se
rious to date in this count
ry with ext
remely high cell concent
rations obse
rved in some locations (>4 ¡Á 10
6 cells L
?1). Toxin levels obse
rved in G
reenshell? mussels (
Perna canaliculus) and Flat oyste
rs (
Ostrea chilensis) exceeded the
regulato
ry level of 0.8 mg/kg shellfish meat as saxitoxin equivalents. Closu
res of comme
rcial shellfish ha
rvesting a
reas we
re enfo
rced fo
r a pe
riod of up to th
ree months as toxin levels
remained above the
regulato
ry level fo
r an extended pe
riod, even afte
r the bloom had c
rashed.
Analysis of several hundred positive shellfish samples during this event allowed us to better understand the technical performance of the method during a bloom event. The periodate screen substantially overestimated the true PST level in the samples because several PSTs gave co-eluting oxidation products, and it was assumed that the entire peak was due to the presence of the more toxic congener. The ratio between the screen and confirmation test results remained relatively constant throughout the bloom events. This information supports an amendment to the overly conservative regulatory control scheme employed in New Zealand for PST testing. Despite overestimation, the periodate screen has proved highly useful as it allows a quick determination of PST-free samples and provides a high level of security against harvesting contaminated products.