**6.** *Planktothrix* **spp. occurrence in Portugal**

*Planktothrix* species can be commonly found in Portuguese freshwater reservoirs. Some of the species reported are *P. mougeotii/P. isothrix* from a wastewater treatment plant in the north of Portugal (Vasconcelos & Pereira 2001, Martins et al. 2010), *P. rubescens* from Beliche reservoir in the South of Portugal (Paulino et al. 2009a) and *P. agardhii* and *P. pseudoagardhii* isolated from several reservoirs in the center and south of Portugal that are maintained in laboratory cultures (Paulino et al. 2009b). However, their occurrence is more pronounced in the center and south of Portugal where it has been increasing and causing problems in some water reservoirs over the last years, such as the deep layer *P. rubescens* bloom with associated microcystin production reported by Paulino et al. 2009. Another example is the particular case of a drinking water reservoir located in the center of Portugal that has been monitored over the last eight years and where a continuous *Planktothrix* spp. bloom persists since 2006 (Fig. 5).

As it can be depicted from Fig. 5 high *Planktothrix* cell concentrations started to appear in the reservoir in 2006 and microcystin concentration increased significantly since 2007. Furthermore, the microcystin concentrations in raw water does not correlate will *Planktothrix* cell numbers, since a high cell concentration does not indicate the presence of high microcystin concentrations and high concentrations of microcystins are not directly associated with high cell densities. This is probably because distinct strains/species of this genus with distinct ability to produce microcystins may occur together. In fact, a natural cyanobacterial population is usually a consortium of toxic and nontoxic strains, and this is believed to be the reason why the population toxicity can vary over time and between samples (WHO, 1999).

Risk Assessment of Cyanobacteria and Cyanotoxins,

the Particularities and Challenges of *Planktothrix* spp. Monitoring 77

years since perennial persistence of *Planktothrix* may occur. In water capture for potable water treatment plants the selection of water off-take depth is important and the infrastructures must be equipped with multiple off-takes. In water reservoirs where *Planktothrix* species occurs, certain particularities must be taken into account (Fig. 6) in order to implement the most adequate risk assessment procedures, monitoring programs and preventive measures to

Fig. 6. Schematic representation of the steps involved in *Planktothrix* risk management.

protect public health from cyanotoxin occurrence in freshwater supplies.

As it can be seen by this monitoring data, *Planktothrix* can suddenly reach high cell densities and dominate the phytoplankton community presenting cell densities values close to total phytoplankton concentration. The figure also shows that *Planktothrix* can form perennial blooms but during this time no visible scum formation was observed within the reservoir. It is still unknown why this bloom of toxic *Planktothrix* persists for 5 years in this reservoir and the answer to this issue will be certainly an important contribution to the knowledge of cyanobacteria ecotoxicology. Since the begining of this P*lanktothrix* bloom this reservoir has been under strict vigilance: monitoring sampling is regular, cellular composition/densities and microcystin content in the samples are always screened and the water treatment plant efficiency analysed to avoid any possible harmfull effect on the population. Nevertheless, due to the persistence of high cell densities and high toxin contents occasionally observed, the reservoir represents a potential risk for human and wild life. Therefore, studies must be performed in order to understand the factors underlying the bloom appearance, persistence and toxicity and to access the risk that this reservoir represents to human health, in order to apply measures to prevent and manage the risk of *Planktothrix* occurrence in the reservoir and to restore the quality of this water-supply.

#### **7. Conclusion**

The risk of human exposure to toxic cyanobacteria is very difficult to assess because many scientific issues remain to be clarified, such as the toxicological properties of cyanotoxins and their real impact on human health. Nevertheless, the establishment of several guidelines for the most common toxins and the establishment of surveillance programs have contributed to minimize the human exposure to toxic cyanobacteria. However, particular attention should be taken for those species, such as *Planktothrix,* that develop particular strategies to adapt, survive and proliferate in freshwater environments. Therefore, the monitoring programs in water reservoirs where *Planktothrix* species occur must have into account that samples should be taken at several depths, microcystin concentration should be accessed constantly and the water system should be monitored regularly throughout the

Fig. 5. *Planktothrix* occurrence in a freshwater reservoir located in the center of Portugal and microcystin-LR concentration in raw water over the same sampling period (---- microcystin concentration in µg.mL -1, light blue bars represent *Planktothrix* spp. cell concentration in nºcells.mL-1, black bars represent total phytoplankton cell concentration in nºcells.mL-1).

As it can be seen by this monitoring data, *Planktothrix* can suddenly reach high cell densities and dominate the phytoplankton community presenting cell densities values close to total phytoplankton concentration. The figure also shows that *Planktothrix* can form perennial blooms but during this time no visible scum formation was observed within the reservoir. It is still unknown why this bloom of toxic *Planktothrix* persists for 5 years in this reservoir and the answer to this issue will be certainly an important contribution to the knowledge of cyanobacteria ecotoxicology. Since the begining of this P*lanktothrix* bloom this reservoir has been under strict vigilance: monitoring sampling is regular, cellular composition/densities and microcystin content in the samples are always screened and the water treatment plant efficiency analysed to avoid any possible harmfull effect on the population. Nevertheless, due to the persistence of high cell densities and high toxin contents occasionally observed, the reservoir represents a potential risk for human and wild life. Therefore, studies must be performed in order to understand the factors underlying the bloom appearance, persistence and toxicity and to access the risk that this reservoir represents to human health, in order to apply measures to prevent and manage the risk of *Planktothrix* occurrence in the reservoir

The risk of human exposure to toxic cyanobacteria is very difficult to assess because many scientific issues remain to be clarified, such as the toxicological properties of cyanotoxins and their real impact on human health. Nevertheless, the establishment of several guidelines for the most common toxins and the establishment of surveillance programs have contributed to minimize the human exposure to toxic cyanobacteria. However, particular attention should be taken for those species, such as *Planktothrix,* that develop particular strategies to adapt, survive and proliferate in freshwater environments. Therefore, the monitoring programs in water reservoirs where *Planktothrix* species occur must have into account that samples should be taken at several depths, microcystin concentration should be accessed constantly and the water system should be monitored regularly throughout the

and to restore the quality of this water-supply.

**7. Conclusion** 

years since perennial persistence of *Planktothrix* may occur. In water capture for potable water treatment plants the selection of water off-take depth is important and the infrastructures must be equipped with multiple off-takes. In water reservoirs where *Planktothrix* species occurs, certain particularities must be taken into account (Fig. 6) in order to implement the most adequate risk assessment procedures, monitoring programs and preventive measures to protect public health from cyanotoxin occurrence in freshwater supplies.

Fig. 6. Schematic representation of the steps involved in *Planktothrix* risk management.

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#### **8. Acknowledgments**

We acknowledge the Ph.D research grant SFRH/BD65706/2009 to Catarina Churro from Fundação para a Ciência e a Tecnologia (Portugal) and the research grant BIC/04/DSA/2008 attributed to Elsa Dias by Instituto Nacional de Saúde Dr. Ricardo Jorge (Portugal).

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**5** 

*Canada* 

**Generalized Additive Models in** 

Jalila Jbilou\* and Salaheddine El Adlouni

*Université de Moncton, Moncton,* 

(1)

**Environmental Health: A Literature Review** 

Time series regression models are especially suitable in epidemiology for evaluating shortterm effects of time-varying exposures. Typically, a single population is assessed with reference to its change over the time in the rate of any health outcome and the corresponding changes in the exposure factors during the same period. In time series regression dependent and independent variables are measured over time, and the purpose is to model the existing relationship between these variables through regression methods. Various applications of these models have been reported in literature exploring relationship between mortality and air pollution (Katsouyanni et al. 2009; Wong et al. 2010; Balakrishnan et al. 2011); hospital admissions and air pollution (Peng et al. 2008; Zanobetti et Schwartz 2009; Lall et al. 2011); pollution plumes and breast cancer (Vieira et a. 2005); diet and cancer (Harnack et al. 1997); and mortality and drinking water (Braga et al. 2001). Different time series methods have been used in these studies, i.e. the linear models (Hatzakis et al. 1986) the log-linear models (Mackenbach et al. 1992), the Poisson regression models (Schwartz et al. 2004), and Generalized Additive Models (Dominici 2002; Wood, 2006). The Generalized Additive Models represent a method of fitting a smooth relationship between two or more variables and are useful for complex correlations, that not easily fitted by standard linear or

The present chapter reviews The Genralized Additive Model (GAM), a class of statistical models which have commonly been used in time series regression, specially allowing for serial correlations, which make them potentially useful for environmental epidemiology.

> *Y X*

where Y is the response variable, X is the matrix (n×p) of the independent p variables

is the vector of the parameters and ε is the vector of errors normally

**1. Introduction** 

non-linear models.

<sup>1</sup> , , *X X <sup>p</sup>* ,

 \*

Corresponding Author

**2. Generalized additive models** 

The classic multiple linear regression model has the form:

